What devices are connected by the system bus? System bus. What does a von Neumann machine consist of?

The main component of every PC is the motherboard (system board). It houses all its main elements - processor, RAM, video card, controllers, as well as slots and connectors for connecting external peripheral devices. All components of the motherboard are interconnected by a system of conductors (lines) through which information is exchanged. This set of lines is called the information bus. A bus that connects only two devices is called port . As an example, consider the structure of, for example, a PC bus:

Interaction between PC components and devices connected to different buses is carried out using so-called bridges implemented on one of the Chipset chips.

PC buses differ in their functional purpose:

- system bus used by Chipset chips to send information to the processor and back;

- cache bus designed to exchange information between the processor and external cache memory;

- memory bus used to exchange information between RAM and processor;

- I/O buses used to exchange information with peripheral devices.

I/O buses are divided into local and standard. Local I/O bus is a high-speed bus designed for exchanging information between high-speed peripheral devices (video adapters, network cards, etc.) and the processor. Currently the local bus is PCI Express(in the past, the AGP bus was used - Accelerated Graphics Port).

Standard The I/O bus is used to connect slower devices (eg mice, keyboards, modems). Until recently, the ISA standard bus was used as this bus. Currently, the USB bus is widely used.

Bus components

The architecture of any bus has the following components:

- data lines(data bus). The data bus provides data exchange between the processor, expansion cards installed in slots and memory. The higher the bus width, the more data can be transferred per clock cycle and the higher the PC performance. Computers with a Pentium family processor have a 64-bit data bus.

- lines for data addressing(address bus). The address bus is used to indicate the address of any device with which the processor exchanges data. Each PC component, each I/O port and RAM cell has its own address.

- data control lines(control bus). A number of service signals are transmitted over the control bus: write/read, readiness to receive/transmit data, confirmation of data receipt, hardware interrupt, control and others. All control bus signals are designed to provide data transmission.

- bus controller, controls the process of exchanging data and service signals and is usually implemented in the form of a separate chip, or in the form of a compatible set of chips - Chipset.

Main characteristics of the tire

Bus width determined by the number of parallel conductors included in it. The first ISA bus for the IBM PC was 8-bit, i.e. it could simultaneously transmit 8 bits. System buses for modern PCs, for example, Pentium IV, are 64-bit.

Bus capacity determined by the number of bytes of information transferred over the bus per second. To determine the bus bandwidth, you need to multiply the bus clock frequency by its bit width. For example, if the bus width is 64 and the clock frequency is 66 MHz, then throughput= 8 (bytes) * 66 MHz = 528 MB/sec.

Bus frequency- this is the clock frequency at which data is exchanged on the bus.

External devices are connected to the buses via an interface.

PC bus standards

The principle of IBM compatibility implies standardization of the interfaces of individual PC components, which, in turn, determines the flexibility of the system as a whole, i.e. the ability to change the system configuration and connect various peripheral devices as necessary. In case of interface incompatibility, controllers are used.

System bus (FSB - Front Side Bus) this bus is designed to exchange information between the processor, memory and other devices included in the system. System buses include GTL , having a bit depth of 64 bits, a clock frequency of 66, 100 and 133 MHz; EV6 , the specification of which allows you to increase its clock frequency to 377 MHz.

I/O buses are being improved in line with the development of PC peripherals.

- ISA bus was considered a PC standard for many years, but is still retained in some PCs today along with the modern PCI bus. Intel, together with Microsoft, has developed a strategy to phase out the ISA bus. Initially, it is planned to eliminate ISA connectors on the motherboard, and subsequently eliminate ISA slots and connect disk drives, mice, keyboards, scanners to the USB bus, and hard drives, CD-ROM, DVD-ROM drives to the IEEE 1394 bus.

- EISA bus became a further development of the ISA bus in the direction of increasing system performance and compatibility of its components. The bus is not widely used due to its high cost and bandwidth, which is inferior to that of the VESA bus that appeared on the market.

- VESA bus or VLB , designed to connect the processor with fast peripheral devices and is an extension of the ISA bus for exchanging video data. During the time of dominance in the computer market CPU processor 80486, the VLB bus was quite popular, but has now been replaced by the more powerful PCI bus.

- PCI bus (Peripheral Component Interconnect bus - interconnection of peripheral components) was developed by Intel for the Pentium processor. The fundamental principle underlying the PCI bus is the use of so-called bridges, which communicate between the PCI bus and other types of buses. The PCI bus implements the Bus Mastering principle, which implies the ability of an external device to control the bus when sending data (without the participation of the processor). During information transfer, a device that supports Bus Mastering takes over the bus and becomes the master. In this case, the central processor is freed up to perform other tasks while data is being transferred. In modern motherboards, the PCI bus clock frequency is set as half the system bus clock frequency, i.e. With a system bus clock speed of 66 MHz, the PCI bus will operate at 33 MHz. Currently, the PCI bus has become the de facto standard among I/O buses.

- AGP bus - high-speed local input/output bus, designed exclusively for the needs of the video system. It connects the video adapter with the PC system memory. The AGP bus was designed based on the PCI bus architecture, so it is also 32-bit. However, she also has additional features increased throughput, in particular through the use of higher clock speeds. If in standard version The 32-bit PCI bus has a clock frequency of 33 MHz, which provides a theoretical PCI throughput of 33 x 32 = 1056 Mbit/s = 132 MB/s, while the AGP bus is clocked by a signal with a frequency of 66 MHz, so its throughput in 1x mode is, 66 x 32 = 264 MB/sec; in 2x mode, the equivalent clock frequency is 132 MHz, and the bandwidth is 528 MB/sec; in 4x mode the throughput is about 1 GB/sec.

- PCI Express – In 2004, Intel developed a sequential PCI-Express bus with a throughput of about 4 Gb/sec. Each device connected to this bus is assigned own channel with a speed indicator of 250Mb/sec. In this case, you can use several channels at once, for example, when transferring data to a video card. Also, the advantages of this bus include the “hot replacement” of any device connected to it, without even turning off the power to the system unit. The high peak performance of the PCI Express bus allows it to be used instead of AGP and PCI buses, and PCI Express is expected to replace these buses in personal computers.

- USB bus (Universal Serial Bus) was designed to connect medium- and low-speed peripheral devices. For example, the information exchange speed on the USB 2.0 bus is 45 MB/s - 60 MB/s. To computers equipped with a USB bus, you can connect peripheral devices such as a keyboard, mouse, joystick, and printer without turning off the power. The USB bus supports Plug & Play technology. When a peripheral device is connected, it is configured automatically.

- SCSI bus (Small Computer System Interface) provides data transfer speeds of up to 320 MB/s and provides for connecting up to eight devices to one adapter: hard drives, CD-ROM drives, scanners, photo and video cameras. Exists wide range SCSI versions ranging from the first version of SCSI I, which provides a maximum throughput of 5 MB/s, to the Ultra 320 version with a maximum throughput of 320 MB/s.

- UDMA bus (Ultra Direct Memory Access - direct connection to memory). UDMA provides data transfer from the hard drive at speeds up to 33.3 MB/sec in mode 2 and 66.7 MB/sec in mode 4.

- IEEE 1394 bus is a high-speed local serial bus standard developed by Apple and Texas Instruments. The IEEE 1394 bus is designed to exchange digital information between PCs and other electronic devices, especially for connecting hard drives and devices for processing audio and video information, as well as work multimedia applications. It is capable of transmitting data at speeds of up to 1600 Mbit/s, working simultaneously with several devices transmitting data from at different speeds, like SCSI. Like USB, IEEE 1394 is fully plug & play capable, including the ability to install components without powering down the PC. Almost any device capable of working with SCSI can be connected to a computer via the IEEE 1394 interface. These include all types of disk drives, including hard drives, optical drives, CD-ROM, DVD, digital video cameras, tape recorders and many other peripheral devices. Thanks to such wide capabilities, this bus has become the most promising for combining a computer with consumer electronics.

Serial and parallel ports

Input and output devices such as a keyboard, mouse, monitor, and printer come standard with a PC. All peripheral input devices must be connected to the PC in such a way that data entered by the user can not only enter the computer correctly, but also be processed efficiently in the future. To exchange data and communicate between peripherals (input/output devices) and the data processing module (motherboard), parallel or serial data transfer can be organized.

Parallel port. A PC usually has 2 parallel ports: LPT1 And LPT2 . You can connect printers and scanners to them. Currently, LPT ports are rarely used, modern printers and scanners are mainly connected to universal USB ports.

Serial ports. A PC usually has 4 serial ports: COM1 – COM4 . These are legacy ports and are rarely used on modern PCs. You can connect to them: an old-style mouse (with a mechanical ball) and some other slow devices.

PS/2– a port for connecting a keyboard and mouse, which was widely used at one time and is still available in many modern computers.

Universal USB port . A variety of devices are connected to USB ports, from printers and scanners to flash drives and external drives, as well as video cameras and webcams, cameras, phones, music players, etc.

PC slots

In order for the motherboard to interact with other separately inserted boards, special sockets called slots are used.

PCI slots. PCI is a standard not only for a slot, but also for the bus itself (the channel through which information is transmitted between computer devices). For a long time, PCI slots have been used to connect external devices ( sound card, network card and other controllers). PCI slots per modern boards three four. They are very easy to find - they are the shortest and usually white, divided by a jumper into two unequal parts. Today, PCI slots are combined with new PCI-Express slots (used to connect video cards).

PCI Express slots. PCI-Express has two types of connection slots additional fees:

Short PCI-Express x1 (data transfer speed – 250 Mb/s)

Long PCI-Express x16 (up to 4 Gb/s) – for connecting a video card.

Installation slots random access memory – they are easy to distinguish among all the connectors; they are equipped with special latches. There can be from two to four of them on the board, which allows you to install from 512 MB to 4 GB of RAM. The slots are strictly tied to the type of RAM, i.e. DDR3 memory cannot be inserted into a slot designed for DDR2 memory. Sometimes there are several slots installed on one motherboard. different types memory.

A complex consisting of a bundle of wires and electronic circuits that ensure the correct transfer of information inside a computer is called a backbone, system bus, or simply tire. The tire is characterized bit depth and frequency.

Maximum amount simultaneously transmitted information is called bus width. The bus width is determined by the processor bit depth and is currently 64 bits. The higher the bus width, the more information it can betray in a unit of time.

The processor searches for a device or memory cell. Each device or cell has its own address. The address is transmitted over the address bus, through which signals are transmitted in one direction from the processor to RAM and devices. The address bus width determines the address space of the processor, i.e. number of memory cells. The number of addressable memory cells is calculated by the formula: N = 2i, Where i– address bus width. If the address bus is 32 bits wide, then the maximum possible number of addressable memory cells is 232 = 4,294,967,296 cells.

Information on the bus is transmitted in the form of pulses electric current. The bus does not operate continuously, but in cycles. The number of bus operation cycles per unit time is called bus frequency.

The bus connects not only the processor and RAM, but virtually all computer devices - disks, keyboard, display, etc. – one way or another, they receive and transmit data through the bus. For this purpose, the bus has standard connectors to which certain computer devices are connected. If there is only one bus, then the I/O throughput is limited. The bus speed is limited by physical factors - the length of the bus and the number of connected devices. Therefore, in modern large systems a complex of interconnected buses is used. Traditionally, buses are divided into buses that provide communication between the processor and memory and I/O buses.

I/O buses can be large, support many types of devices, and usually follow one bus standard. Processor-memory buses are relatively short, high-speed and correspond to the organization of the memory system to ensure maximum throughput of the memory-processor channel.

Some computers have a single bus for memory and input/output devices. This tire is called systemic. Local A bus is a bus that electrically connects directly to the contacts of the microprocessor. It usually combines the processor, memory, buffering circuits for the system bus and its controller, as well as some auxiliary circuits.

Initially, the ISA bus was used (8- and 16-bit, frequency 8 MHz), created in the early 80s and having low bandwidth. Nowadays the ISA bus is sometimes used to connect low-speed devices (keyboard, mouse, etc.).

Currently more often used:

ü PCI bus (Peripheral Component Interconnect bus – bus for interaction of peripheral devices);

ü AGP (Accelerated Craphic Port) graphics bus;

ü HyperTransport – high-speed bus for connecting internal devices computer system. The clock frequency reaches 800 MHz. Bandwidth is up to 6.4 GB/s;

ü USB is designed to connect up to 256 external devices (such as a mouse, printer, scanner, camera, FM tuner, etc.) to one USB channel (based on the common bus principle). Bandwidth up to 480 Mbps (USB 2.0 version).

In modern computers, the processor frequency can exceed the system bus frequency (processor frequency is 1 GHz, and the bus frequency is 100 MHz).

Components within a PC interact with each other in various ways. Most internal components, including the processor, cache, memory, expansion cards, and storage devices, communicate with each other using one or more tires(buses).

A bus in computers is a channel through which information is transferred between two or more devices (usually a bus that connects only two devices is called port- port). A bus typically has access points, or places that a device can connect to to make itself part of the bus, and devices on the bus can send information to and receive information from other devices. The concept of a bus is quite general both for the “inside” of the PC and for the outside world. For example, a telephone connection in a house can be thought of as a bus: information travels along wires in the house, and one can connect to the "bus" by installing a telephone jack, plugging a telephone into it, and picking up the telephone. All phones on the bus can share information, i.e. speech.

This material is dedicated to the tires of modern PCs. First, tires and their characteristics are discussed, and then the most common tires in the world are discussed in detail. I/O buses(Input/Output bus), also called expansion buses(expansion buses).

Tire functions and characteristics

PC buses are the main data "paths" on the motherboard. The main one is system bus(system bus), which connects the processor and main memory RAM. Previously, this bus was called local, but in modern PCs it is called front tire(Front Side Bus - FSB). The characteristics of the system bus are determined by the processor; The modern system bus is 64 bits wide and operates at 66, 100 or 133 MHz. Such high frequency signals create electrical noise and other problems. Therefore, the frequency must be reduced so that the data reaches expansion cards(expansion card), or adapters(adapters), and other more remote components.

However, the first PCs had only one bus, which was shared by the processor, RAM memory, and I/O components. Processors of the first and second generations operated at a low clock frequency and all system components could support this frequency. In particular, this architecture made it possible to expand RAM capacity using expansion cards.

In 1987, Compaq developers decided to separate the system bus from the I/O bus so that they could operate at different speeds. Since then, this multi-bus architecture has become the industry standard. Moreover, modern PCs have several I/O buses.

Tire hierarchy

The PC has a hierarchical organization of various buses. Most modern PCs have at least four buses. The bus hierarchy is explained by the fact that each bus is increasingly moving away from the processor; Each bus connects to the level above it, integrating various PC components. Each bus is usually slower than the bus above it (for the obvious reason - the processor is the fastest device in the PC):

• Internal cache bus: This is the fastest bus that connects the processor and the internal L1 cache.
• System bus: This is the second level system bus that connects the memory subsystem to the chipset and processor. On some systems, the processor and memory buses are the same thing. This bus operated at a speed (clocking frequency) of 66 MHz until 1998, and then it was increased to 100 MHz and even 133 MHz. Pentium II and higher processors implement an architecture with double independent bus(Dual Independent Bus - DIB) - the single system bus is replaced by two independent buses. One of them is intended for accessing main memory and is called front tire(frontside bus), and the second one is for accessing the L2 cache and is called rear tire(backside bus). The presence of two buses increases the performance of the PC, since the processor can simultaneously receive data from both buses. In fifth-generation motherboards and chipsets, the L2 cache is connected to the standard memory bus. Note that the system bus is also called main bus(main bus), processor bus(processor bus), memory bus(memory bus) and even local bus(local bus).
• Local I/O bus: This high-speed I/O bus is used to connect fast peripheral devices to the memory, chipset, and processor. This bus is used by video cards, disk drives and network interfaces. The most common local I/O buses are the VESA Local Bus (VLB) and the Peripheral Component Interconnect (PCI) bus.
• Standard I/O bus: The “deserved” standard I/O bus is connected to the three buses considered, which is used for slow peripheral devices (mouse, modem, sound cards, etc.), as well as for compatibility with older devices. In almost all modern PCs, such a bus is the ISA (Industry Standard Architecture) bus.
• Universal Serial Bus(Universal Serial Bus - USB), allowing you to connect up to 127 slow peripheral devices using hub(hub) or daisy-chaining devices.
• High-speed serial bus IEEE 1394 (FireWire), designed for connecting digital cameras, printers, televisions and other devices that require extremely high bandwidth to a PC.

Multiple I/O buses connecting various peripherals to the processor are connected to the system bus using bridge(bridge), implemented in the chipset. The system chipset manages all buses and ensures that every device in the system communicates correctly with every other device.

New PCs have an additional "bus" that is specifically designed for graphical interaction only. In fact, this is not a tire, but port- Accelerated Graphics Port (AGP). The difference between a bus and a port is that a bus is usually designed to share media between multiple devices, while a port is designed to only share two devices.

As shown earlier, I/O buses are actually an extension of the system bus. On the motherboard, the system bus ends at the chipset chip, which forms a bridge to the I/O bus. Buses play a vital role in data exchange in a PC. In fact, all PC components, with the exception of the processor, communicate with each other and the system RAM through various I/O buses, as shown in the figure on the left.

Address and data buses

Each tire consists of two different parts: data bus(data bus) and address bus(address bus). When most people talk about a bus, they think of a data bus; The data itself is transmitted along the lines of this bus. The address bus is a set of lines whose signals determine where to send or receive data.

Of course, there are signal lines to control the operation of the bus and signal the availability of data. Sometimes these lines are called control bus(control bus), although they are often not mentioned.

Tire width

A bus is a channel through which information “flows.” The wider the bus, the more information can "flow" along the channel. The first ISA bus on the IBM PC was 8 bits wide; the general purpose ISA bus currently in use is 16 bits wide. Other I/O buses, including VLB and PCI, are 32 bits wide. The system bus width on PCs with Pentium processors is 64 bits.

The width of the address bus can be determined independently of the width of the data bus. The address bus width indicates how many memory cells can be addressed during data transfer. In modern PCs, the address bus width is 36 bits, which allows addressing memory with a capacity of 64 GB.

Bus speed

Bus speed(bus speed) shows how many bits of information can be transmitted on each bus conductor per second. Most buses carry one bit per clock cycle on a single wire, although newer buses such as AGP can carry two bits of data per clock cycle, doubling the performance. The old ISA bus requires two clock cycles to transfer one bit, cutting performance in half.

Bus bandwidth

Width (bits) Speed ​​(MHz) Throughput (MB/s) 8-bit ISA 16-bit ISA 64-bit PCI 2.1 AGP (x2 mode) AGP (x4 mode)

Bandwidth(bandwidth) also called throughput(throughput) and shows the total amount of data that can be transferred over the bus in a given unit of time. The table shows theoretical bandwidth of modern I/O buses. In fact, the tires do not reach the theoretical value due to overhead for executing commands and other factors. Most tires can operate at different speeds; The following table shows the most typical values.

Let us make a note regarding four last lines. Theoretically, the PCI bus can be expanded to 64 bits and 66 MHz speed. However, for compatibility reasons, almost all PCI buses and devices on the bus are only rated at 33 MHz and 32 bits. AGP builds on the theoretical standard and operates at 66 MHz, but retains a 32-bit width. AGP has additional modes x2 and x4, which allow the port to perform data transfers two or four times per clock cycle, increasing the effective bus speed to 133 or 266 MHz.

Bus interface

In a multi-bus system, the chipset must provide circuitry to combine the buses and communicate between a device on one bus and a device on another bus. Such schemes are called bridge(bridge) (note that a bridge is also a network device for connecting two different types of networks). The most common is the PCI-ISA bridge, which is a component of the system chipset for PCs with Pentium processors. The PCI bus also has a bridge to the system bus.

Bus mastering

In high-capacity buses, a huge amount of information is transmitted over the channel every second. Typically a processor is required to manage these transfers. In effect, the processor acts as a "middleman" and, as is often the case in the real world, it is much more efficient to remove the middleman and perform the transfers directly. For this purpose, devices have been developed that can control the bus and act independently, i.e. transfer data directly to system RAM memory; such devices are called driving tires(bus masters). Theoretically, the processor can perform other work simultaneously with data transfers on the bus; In practice, the situation is complicated by several factors. For correct implementation bus mastering(bus mastering) arbitration of bus requests is required, which is provided by the chipset. Bus mastering is also called "first party" DMA, since the operation is controlled by the device performing the transfer.

Currently, bus mastering is implemented on the PCI bus; Support has also been added for IDE/ATA hard drives to implement bus mastering on PCI under certain conditions.

Local bus principle

The beginning of the 90s is characterized by the transition from text-based applications to graphical ones and the growing popularity of operating systems. Windows systems. This has led to a huge increase in the amount of information that must be transferred between the processor, memory, video and hard drives. A standard monochromatic (black and white) text screen contains only 4,000 bytes of information (2,000 for character codes and 2,000 for screen attributes), but a standard 256-color Windows screen requires over 300,000 bytes! Moreover, modern resolution of 1600x1200 with 16 million colors requires 5.8 million bytes of information per screen!

The transition of the software world from text to graphics also meant increased program sizes and increased memory requirements. From an I/O perspective, processing the additional data for a video card and huge capacity hard drives requires much more I/O bandwidth. This situation had to be faced with the advent of the 80486 processor, the performance of which was much higher than previous processors. The ISA bus no longer met the increased requirements and became a bottleneck in increasing PC performance. Increasing the speed of a processor does little if it must wait on a slow system bus to transfer data.

The solution was found in the development of a new, faster bus, which was supposed to complement the ISA bus and be used specifically for such high-speed devices as video cards. This bus had to be placed on (or near) the much faster memory bus and run at approximately the external speed of the processor in order to transfer data much faster than the standard ISA bus. When such devices were placed near ("locally") the processor, local bus. The first local bus was the VESA Local Bus (VLB), and the modern local bus in most PCs is the Peripheral Component Interconnect (PCI) bus.

System bus

System bus(system bus) connects the processor to the main RAM memory and, possibly, to the L2 cache. It is the central bus of the computer and the other buses “branch” from it. The system bus is implemented as a set of conductors on the motherboard and must match specific type processor. It is the processor that determines the characteristics of the system bus. At the same time, the faster the system bus, the faster the remaining electronic components of the PC must be.

Old CPUs Tire width Bus speed 8088 8 bits 4.77 MHz 8086 16 bits 8 MHz 80286-12 16 bits 12 MHz 80386SX-16 16 bits 16 MHz 80386DX-25 32 bits 25 MHz

Let's consider system buses of a PC with processors of several generations. In processors of the first, second and third generations, the system bus frequency was determined by the operating frequency of the processor. As processor speed increased, so did the system bus speed. At the same time, the address space increased: in the 8088/8086 processors it was 1 MB (20-bit address), in the 80286 processor the address space was increased to 16 MB (24-bit address), and starting with the 80386 processor the address space was 4 GB (32 -bit address).

Family 80486 Tire width Bus speed 80486SX-25 32 bits 25 MHz 80486DX-33 32 bits 33 MHz 80486DX2-50 32 bits 25 MHz 80486DX-50 32 bits 50 MHz 80486DX2-66 32 bits 33 MHz 80486DX4-100 32 bits 40 MHz 5X86-133 32 bits 33 MHz

As can be seen from the table for fourth-generation processors, the system bus speed initially corresponded to the operating frequency of the processor. However, technological advances made it possible to increase the processor frequency, and matching the system bus speed required increasing the speed of external components, mainly system memory, which was associated with significant difficulties and cost restrictions. Therefore, the 80486DX2-50 processor was used for the first time frequency doubling(clock doubling): the processor worked with internal clock frequency 50 MHz, and external The system bus speed was 25 MHz, i.e. only half the operating frequency of the processor. This technique significantly improves computer performance, especially due to the presence of an internal L1 cache, which satisfies most of the processor's access to system memory. Since then frequency multiplication(clock multiplying) has become a standard way to improve computer performance and is used in all modern processors, and the frequency multiplier is increased to 8, 10 or more.

Pentium family Tire width Bus speed Intel P60 64 bits 60 MHz Intel P100 64 bits 66 MHz Cyrix 6X86 P133+ 64 bits 55 MHz AMD K5-133 64 bits 66 MHz Intel P150 64 bits 60 MHz Intel P166 64 bits 66 MHz Cyrix 6X86 P166+ 64 bits 66 MHz Pentium Pro 200 64 bits 66 MHz Cyrix 6X86 P200+ 64 bits 75 MHz Pentium II 64 bits 66 MHz

For a long time, PC system buses with fifth-generation processors operated at speeds of 60 MHz and 66 MHz. A significant step forward was the increase in data width to 64 bits and the expansion of the address space to 64 GB (36-bit address).

The system bus speed was increased to 100 MHz in 1998 thanks to the development of production of PC100 SDRAM chips. RDRAM memory chips can further increase the speed of the system bus. However, the transition from 66 MHz to 100 MHz had a significant impact on processors and motherboards with Socket 7. In Pentium II modules, up to 70-80% of traffic (information transfers) is carried out inside the new SEC (Single Edge Cartridge), which houses the processor and both caches are L1 cache and L2 cache. This cartridge operates at its own speed, independent of the system bus speed.

CPU Chipset Speed tires CPU speed Intel Pentium II 82440BX 82440GX 100 MHz 350,400,450 MHz AMD K6-2 Via MVP3, Aladdin V 100 MHz 250,300,400 MHz Intel Pentium II Xeon 82450NX 100 MHz 450.500 MHz Intel Pentium III i815 i820 133 MHz 600.667+ MHz AMD Athlon VIA KT133 200 MHz 600 - 1000 MHz

The i820 and i815 chipsets, designed for the Pentium III processor, are designed for a 133 MHz system bus. Finally, the AMD Athlon processor introduced significant changes to the architecture and the concept of a system bus turned out to be unnecessary. This processor can work with different types RAM at a maximum frequency of 200 MHz.

Types of I/O buses

This section will cover various I/O buses, with much of it dedicated to modern buses. A general idea of ​​the use of I/O buses is given by the following figure, which clearly shows the purpose of the various I/O buses of a modern PC.

The following table summarizes the various I/O buses used in modern PCs:

Tire	Year	Width	Speed	Max. checkpoint ability
PC and XT	1980-82	8 bits	Synchronous: 4.77-6 MHz	4-6 MB/s
ISA (AT)	1984	16 bits	Synchronous: 8-10 MHz	8 MB/s
M.C.A.	1987	32 bits	Asynchronous: 10.33 MHz	40 MB/s
EISA (for servers)	1988	32 bits	Synchronous: max. 8 MHz	32 MB/s
VLB, for 486	1993	32 bits	Synchronous: 33-50 MHz	100-160 MB/s
PCI	1993	32/64 bit	Asynchronous: 33 MHz	132 MB/s
USB	1996	Sequential		1.2 MB/s
FireWire (IEEE1394)	1999	Sequential		80 MB/s
USB 2.0	2001	Sequential		12-40 MB/s

Old tires

The new modern PCI bus and AGP port were “born” from old buses that can still be found in PCs. Moreover, the oldest ISA bus is still used even in the latest PCs. Next we will look at the old PC tires in a little more detail.

Industry Standard Architecture (ISA) bus

This is the most common and truly standard bus for PCs, which is used even in the latest computers despite the fact that it has remained virtually unchanged since its expansion to 16 bits in 1984. Of course, it is now supplemented by faster buses, but it “survives” thanks to the presence of a huge base of peripheral equipment designed for this standard. In addition, there are many devices for which ISA speed is more than enough, such as modems. According to some experts, it will take at least 5-6 years before the ISA bus “dies”.

The choice of the width and speed of the ISA bus was determined by the processors with which it worked in the first PCs. The original ISA bus on the IBM PC was 8 bits wide, corresponding to the 8 bits of the external data bus of the 8088 processor, and ran at 4.77 MHz, which is also the speed of the 8088 processor. In 1984, the IBM AT computer appeared with an 80286 processor and the bus width was doubled up to 16 bits, like the external data bus of the 80286 processor. At the same time, the bus speed was increased to 8 MHz, which also matched the speed of the processor. Theoretically, the bus throughput is 8 MB/s, but in practice it does not exceed 1-2 MB/s.

In modern PCs, the ISA bus acts as internal bus, which is used for keyboard, floppy disk, serial and parallel ports, and how external expansion bus, to which you can connect 16-bit adapters, such as a sound card.

Subsequently, AT processors became faster, and then their data bus was increased, but now the requirement for compatibility with existing devices forced manufacturers to adhere to the standard and the ISA bus has remained virtually unchanged since then. The ISA bus provides sufficient bandwidth for slow devices and is sure to guarantee compatibility with almost every PC released.

Many expansion cards, even modern ones, are still 8-bit (you can tell by the card's connector - 8-bit cards only use the first part of the ISA connector, while 16-bit cards use both parts). For these cards, the low bandwidth of the ISA bus does not matter. However, access to interrupts IRQ 9 through IRQ 15 is provided through wires in the 16-bit portion of the bus connectors. This is why most modems cannot be connected to IRQs with large numbers. IRQ lines between ISA devices cannot be shared.

Document The PC99 System Design Guide, prepared by Intel and Microsoft, categorically requires the removal of ISA bus slots from motherboards, so we can expect that the days of this “well-deserved” bus are numbered.

MicroChannel Architecture (MCA) bus

This bus was IBM's attempt to make the ISA bus "bigger and better." When the 80386DX processor with a 32-bit data bus was introduced in the mid-1980s, IBM decided to develop a bus to match this data bus width. The MCA bus was 32 bits wide and had several advantages over the ISA bus.

The MCA bus had some great features considering it was introduced in 1987 i.e. seven years before the advent of the PCI bus with similar capabilities. In some respects, the MCA bus was simply ahead of its time:

• Width 32 bits: The bus was 32 bits wide, like the local VESA and PCI buses. Its throughput was much higher compared to the ISA bus.
• Bus mastering: The MCA bus effectively supported bus mastering adapters, including proper bus arbitration.
• The MCA bus automatically configured the adapter cards, making jumpers unnecessary. This happened 8 years before Windows 95 made PnP technology generally accepted on PCs.

The MCA bus had enormous potential. Unfortunately, IBM made two such decisions that did not promote the adoption of this bus. Firstly, the MCA bus was incompatible with the ISA bus, i.e. ISA cards did not work at all in PCs with an MCA bus, and the computer market is very sensitive to the problem of backward compatibility. Secondly, IBM decided to make the MCA bus its own without licensing its use.

These two factors, combined with the higher cost of MCA bus systems, led to the oblivion of the MCA bus. Since PS/2 computers are no longer in production, the MCA bus is "dead" for the PC market, although IBM still uses it in its RISC 6000 UNIX servers. The MCA bus story is one of the classic examples of how in the world of computers non-technical issues often dominate technical issues.

Extended Industry Standard Architecture (EISA) bus

This bus never became as standard as the ISA bus and was not widely used. In fact, it was Compaq's answer to the MCA bus and led to similar results.

Compaq avoided two of IBM's biggest mistakes when developing the EISA bus. Firstly, the EISA bus was compatible with the ISA bus and, secondly, all PC manufacturers were allowed to use it. In general, the EISA bus had significant technical advantages over the ISA bus, but the market did not accept it. Main features of the EISA bus:

• ISA bus compatibility: ISA cards could work in EISA slots.
• Bus width 32 bits: Bus width increased to 32 bits.
• Bus mastering: The EISA bus effectively supported bus mastering adapters, including proper bus arbitration.
• Plug and Play (PnP) technology: The EISA bus automatically configured adapter cards similar to the PnP standard of modern systems.

EISA-based systems are now sometimes found in network file servers, but it is not used in desktop PCs due to higher costs and the lack of a wide selection of adapters. Finally, its throughput is significantly inferior to local buses VESA Local Bus and PCI. In fact, the EISA bus is now close to dying.

VESA Local Bus (VLB)

The first one is quite popular local bus VESA Local Bus (VL-Bus or VLB) appeared in 1992. The abbreviation VESA stands for Video Electronics Standards Association, and this association was created in the late 80s to solve the problems of video systems in PCs. The main reason for the development of the VLB bus was to improve the performance of PC video systems.

The VLB bus is a 32-bit bus that is a direct extension of the 486 processor's memory bus. The VLB bus slot is a 16-bit ISA slot with a third and fourth slot added at the end. The VLB typically operates at 33 MHz, although higher speeds are possible on some systems. Since it is an extension of the ISA bus, an ISA card can be used in a VLB slot, but it makes sense to occupy the normal ISA slots first and leave a small number of VLB slots for VLB cards, which of course do not work in ISA slots. The use of a VLB graphics card and I/O controller significantly improves system performance compared to a system with only a single ISA bus.

Despite the fact that the VLB bus was very popular in PCs with the 486 processor, the advent of the Pentium processor and its local PCI bus in 1994 led to the gradual "oblivion" of the VLB bus. One of the reasons for this was Intel's efforts to promote the PCI bus, but there were also several technical problems associated with the implementation of VLB. First, the bus design is very much tied to the 486 processor, and the move to Pentium caused compatibility issues and other problems. Secondly, the tire itself had technical shortcomings: small number of cards on the bus (often two or even one), synchronization problems when using multiple cards, and lack of support for bus mastering and Plug and Play technology.

Now the VLB bus is considered obsolete and even the latest motherboards with a 486 processor use the PCI bus, while Pentium processors use only PCI. However, PCs with a VLB bus are inexpensive and can sometimes still be found.

Peripheral Component Interconnect (PCI) bus

The most popular I/O bus right now interactions between peripheral components(Peripheral Component Interconnect - PCI) was developed by Intel in 1993. It was aimed at fifth and sixth generation systems, but was also used in the latest generation of motherboards with the 486 processor.

Like the VESA Local Bus, the PCI bus is 32 bits wide and typically runs at 33 MHz. The main advantage of PCI over VESA bus Local Bus lies in the chipset that controls the bus. The PCI bus is controlled by special circuitry in the chipset, and the VLB bus was basically just an extension of the 486 processor bus. The PCI bus is not "tied" to the 486 processor in this regard, and its chipset provides proper bus control and bus arbitration, allowing PCI to do much more than the VLB bus could. The PCI bus is also used outside the PC platform, providing versatility and reducing the cost of system development.

In modern PCs, the PCI bus acts as internal bus which connects to the EIDE channel on the motherboard, and how external expansion bus, which has 3-4 expansion slots for PCI adapters.

The PCI bus is connected to the system bus through a special “bridge” and operates at a fixed frequency regardless of the processor clock frequency. It is limited to five expansion slots, but each of them can be replaced with two devices built into the motherboard. The processor can also support multiple bridge chips. The PCI bus is more strictly specified than the VL-Bus and provides several additional capabilities. In particular, it supports cards with a supply voltage of +3.3 V and 5 V, using special keys that prevent the card from being inserted into the wrong slot. Next, the operation of the PCI bus is discussed in more detail.

PCI bus performance

The PCI bus actually has the highest performance among common I/O buses in modern PCs. This is due to several factors:

• Burst mode: The PCI bus can transfer information in burst mode, where after initial addressing, several sets of data can be transferred in a row. This mode is similar to cache bursting.
• Bus mastering: The PCI bus supports full mastering, which improves performance.
• High Bandwidth Options: Version 2.1 of the PCI bus specification allows expansion to 64 bits and 66 MHz, increasing current performance by four times. In practice, the 64-bit PCI bus has not yet been implemented in the PC (although it is already used in some servers) and the speed is currently limited to 33 MHz, mainly due to compatibility issues. For some time you will have to limit yourself to 32 bits and 33 MHz. However, thanks to AGP, higher performance will be realized in a slightly modified form.

Depending on the chipset and motherboard, the PCI bus speed can be set as synchronous or asynchronous. In a synchronous setup (used on most PCs), the PCI bus operates at half the speed of the memory bus; since the memory bus typically runs at 50, 60, or 66 MHz, the PCI bus runs at 25, 30, or 33 MHz. At asynchronous setup The PCI bus speed can be set independently of the memory bus speed. This is usually controlled using jumpers on the motherboard or BIOS settings. Overclocking the system bus on a PC that uses a synchronous PCI bus will overclock the PCI peripherals, often causing system instability problems.

The original implementation of the PCI bus ran at 33 MHz, and the subsequent PCI 2.1 specification specified a frequency of 66 MHz, which corresponds to a throughput of 266 MB/s. The PCI bus can be configured for 32- and 64-bit data widths and allows for 32- and 64-bit cards, as well as interrupt sharing, which is useful in high-performance systems that lack IRQ lines. Since mid-1995, all high-speed PC devices have been communicating with each other via the PCI bus. Most often it is used for hard drive controllers and graphics controllers, which are mounted directly on the motherboard or on expansion cards in PCI bus slots.

PCI bus expansion slots

The PCI bus allows more expansion slots than the VLB bus without causing technical problems. Most PCI systems support 3 or 4 PCI slots, and some support significantly more.

Note: On some systems, not all slots support bus mastering. This is less common now, but it is still recommended to look at the motherboard manual.

The PCI bus allows for a greater variety of expansion cards compared to the VLB bus. The most common types are video cards, SCSI host adapters, and high-speed network cards. (Hard drives also operate on the PCI bus, but they are usually connected directly to the motherboard.) Note, however, that the PCI bus does not implement some functions; for example, serial and parallel ports must remain on the ISA bus. Fortunately, even today the ISA bus remains more than sufficient for these devices.

PCI bus internal interrupts

The PCI bus uses its internal interrupt system to handle requests from cards on the bus. These interrupts are often called "#A", "#B", "#C" and "#D" to avoid confusion with the normally numbered system IRQs, although they are sometimes also called "#1" through "#4". These interrupt levels are usually invisible to the user except on the screen BIOS settings for PCI, where they can be used to control the operation of PCI cards.

These interrupts, if required by the cards in the slots, are mapped to regular interrupts, most often to IRQ9 - IRQ12. PCI slots on most systems can be mapped to most of the four common IRQs. On systems that have more than four PCI slots or have four slots and USB controller(which uses PCI) two or more PCI devices share an IRQ.

PCI bus mastering

Recall that bus mastering is the ability of devices on the PCI bus (different, of course, from the system chipset) to take control of the bus and directly perform transfers. The PCI bus was the first bus that led to the popularity of bus mastering (probably because the operating system and programs were able to take advantage of it).

The PCI bus supports full bus mastering and provides a means of bus arbitration through the system chipset. The PCI design allows multiple devices to master the bus at the same time, and the arbitration circuit ensures that no device on the bus (including the processor!) will block any other device. However, one device is allowed to use the full bandwidth of the bus if no other devices are transmitting anything. In other words, the PCI bus acts like a tiny local area network inside a computer in which multiple devices can communicate with each other, sharing communication channel, and which is controlled by the chipset.

Plug and Play technology for PCI bus

The PCI bus is part of the Plug and Play (PnP) standard developed by Intel, Microsoft, and many others. PCI bus systems were the first to popularize the use of PnP. PCI chipset circuits manage card identification and work with the operating system and BIOS to automatically allocate resources to compatible cards.

The PCI bus is constantly being improved and development is led by the PCI Special Interest Group, which includes Intel, IBM, Apple, and others. The result of these developments was an increase in the bus frequency to 66 MHz and data expansion to 64 bits. However, alternatives are also being created, such as Accelerated Graphics Port (AGP) and FireWire (IEEE 1394) high-speed serial bus. AGP is actually a 66 MHz PCI bus (version 2.1) that introduces some improvements aimed at graphics systems.

Another initiative is the tire PCI-X, also called "Project One" and "Future I/O". IBM, Mylex, 3Com, Adaptec, Hewlett-Packard and Compaq want to develop a special high-speed server version of the PCI bus. This bus will have a bandwidth of 1 GB/s (64 bits, 133 MHz). Intel and Dell Computer are not involved in this project.

Dell Computer, Hitachi, NEC, Siemens, Sun Microsystems and Intel, in response to Project One, took the initiative to develop the Next-Generation I/O bus ( NGIO), targeting a new I/O architecture for servers.

In August 1999, seven leading companies (Compaq, Dell, Hewlett-Packard, IBM, Intel, Microsoft, Sun Microsystems) announced their intention to combine the best ideas of Future I/O and Next Generation I/O buses. The new open I/O architecture for servers should provide throughput of up to 6 GB/s. Expected that new standard The NGIO will be adopted at the end of 2001.

Accelerated graphics port

The need to increase the bandwidth between the processor and the video system initially led to the development of a local I/O bus in the PC, starting with the VESA Local Bus and ending with the modern PCI bus. This trend continues, with the demand for increased video bandwidth no longer being met even by the PCI bus with its standard 132 MB/s bandwidth. 3D graphics(3D graphics) allows you to simulate virtual and real worlds on the screen with the smallest details. Displaying textures and hiding objects requires huge amounts of data, and the graphics card must have quick access to this data in order to maintain high refresh rates.

Traffic on the PCI bus becomes very busy in modern PCs when video, hard drives and other peripherals compete for the only I/O bandwidth. To prevent saturation of the PCI bus with video information, Intel developed a new interface specifically for the video system, called accelerated graphics port(Accelerated Graphics Port - AGP).

The AGP port is designed in response to the increasing demand for video performance. As programs and computers use areas such as 3D acceleration and full-motion video playback, the processor and video chipset must process more and more information. In such applications, the PCI bus has reached its limit, especially since it is also used by hard drives and other peripheral devices.

In addition, more and more video memory is required. For 3D graphics you need more memory and not only for screen images, but also for calculations. Traditionally, this problem is solved by placing more and more memory on the video card, but this poses two problems:

• Price: Video memory is more expensive than regular RAM memory.
• Limited Capacity: The memory capacity on a video card is limited: if you put 6 MB on the card and 4 MB is required for the frame buffer, then there is only 2 MB left for processing. This memory is not easy to expand and cannot be used for anything else unless video processing is needed.

AGP solves these problems by allowing the video processor to access main system memory to perform calculations. This technique is much more efficient because this memory can be dynamically shared between the system processor and video processor depending on the needs of the system.

The idea behind implementing AGP is quite simple: to create a fast, specialized interface between the video chipset and the system processor. The interface is implemented only between these two devices, which provides three main advantages: it is easier to implement the port, it is easier to increase AGP speed, and video-specific enhancements can be introduced into the interface. The AGP chipset acts as an intermediary between the processor, Pentium II L2 cache, system memory, video card and PCI bus, implementing the so-called quad port(Quad Port).

AGP is considered a port, not a bus, since it only connects two devices (the processor and the video card) and does not allow expansion. One of the main advantages of AGP is that it isolates the video system from the rest of the PC components, eliminating competition for bandwidth. Since the graphics card is removed from the PCI bus, other devices can run faster. For AGP, the motherboard has a special socket, which is similar to the PCI bus socket, but is located in a different location on the board. In the following figure, you can see two ISA bus sockets (black), then two PCI bus sockets (white) and an ADP socket (brown).

AGP appeared at the end of 1997 and was the first to be supported by the 440LX Pentium II chipset. The following year, AGP chipsets from other companies appeared. For more information about AGP, see the website http://developer.intel.com/technology/agp/.

AGP interface

The AGP interface is similar to the PCI bus in many respects. The slot itself has the same physical shape and dimensions, but is offset further from the edge of the motherboard than PCI slots. The AGP specification actually relies on the PCI 2.1 specification, which allows 66 MHz speeds, but this speed is not implemented in the PC. Maternal AGP boards They have one expansion slot for an AGP video card and one less PCI slot, but otherwise are similar to PCI motherboards.

Bus width, speed and bandwidth

The AGP bus is 32 bits wide, just like the PCI bus, but instead of running at half the memory bus speed like PCI does, it runs at full speed. For example, on a standard Pentium II motherboard, the AGP bus runs at 66 MHz instead of the 33 MHz PCI bus. This immediately doubles the port's bandwidth - instead of the 132 MB/s limit for PCI, the AGP port has a bandwidth of 264 MB/s in the lowest speed mode. Additionally, it does not share any bandwidth with other PCI bus devices.

In addition to doubling the bus speed, AGP defines a mode 2X, which uses special signals, allowing twice as much data to be transmitted through the port at the same clock frequency. In this mode, information is transmitted on the rising and falling edges of the synchronization signal. While the PCI bus only transmits data on one edge, AGP transmits data on both edges. As a result, performance doubles further and theoretically reaches 528 MB/s. It is also planned to implement the regime 4X, in which four transfers are carried out in each clock cycle, which will increase performance to 1056 MB / s.

Of course, all this is impressive and the bandwidth of 1 GB/s is very good for a video card, but there is one problem: a modern PC has several buses. Recall that Pentium-class processors have a 64-bit data bus width and operate at 66 MHz, which provides a theoretical throughput of 524 MB/s, so 1 GB/s bandwidth does not provide a significant gain unless the data bus speed is increased beyond 66 MHz . New motherboards have increased the system bus speed to 100 MHz, which increases throughput to 800 MB/s, but this is not enough to justify mode transfers 4X.

In addition, the processor must access system memory, not just the video system. If the entire system bandwidth of 524 MB/s is occupied by video via AGP, what can the processor do? In this case, moving to a system speed of 100 MHz will provide some benefit.

AGP Port Video Pipelining

One of the benefits of AGP is its ability to pipeline data requests. Pipelining was first used in modern processors as a way to improve performance by overlapping sequential chunks of tasks. Thanks to AGP, the video chipset can use a similar technique when requesting information from memory, which significantly improves performance.

AGP access to system memory

The most important feature of AGP is the ability to share the main system memory with the video chipset. This allows the video system to access more memory for 3D graphics and other processing without requiring large amounts of video memory on the video card. Memory on the video card is shared between the frame buffer and other uses. Because the framebuffer requires high-speed and dear memory, such as VRAM, in most cards all memory is executed in VRAM, although this is required for memory areas other than the framebuffer.

Note that AGP Not refers to the unified memory architecture (UMA). In this architecture all The video card memory, including the frame buffer, is taken from the main system memory. In AGP, the frame buffer remains on the video card, where it is located. The frame buffer is the most important component of video memory and requires the highest performance, so it makes more sense to leave it on the video card and use VRAM for it.

AGP allows the video processor to access system memory for other memory-intensive tasks, such as texturing and other 3D graphics operations. This memory is not as critical as the frame buffer, which allows video cards to be cheaper by reducing VRAM memory capacity. Accessing system memory is called direct execution from memory(DIrect Memory Execute - DIME). A special device called graphic aperture remapping table(Graphics Aperture Remapping Table - GART), operates on RAM addresses in such a way that they can be distributed in system memory in small blocks, rather than one large section, and provides them to the video card as if it were part of video memory. A visual representation of AGP functions is given by the following figure:

AGP requirements

To use AGP in a system, several requirements must be met:

• Availability of AGP video card: This requirement is quite obvious.
• Availability of a motherboard with an AGP chipset: Of course, the chipset on the motherboard must support AGP.
• Operating system support: The operating system must support the new interface using its internal drivers and routines.
• Driver support: Of course, the video card requires special drivers to support AGP and use it special abilities, for example mode 3X.

New serial buses

For 20 years now, many peripheral devices have been connected to the same parallel and serial ports that appeared on the first PC, and with the exception of the Plug and Play standard, “I/O technology” has changed little since 1081. However, by the end of the 90s of the last century, users increasingly began to feel the limitations of standard parallel and serial ports:

• Bandwidth: Serial ports have a maximum throughput of 115.2 Kb/s, and parallel ports (depending on type) about 500 Kb/s. However, devices such as digital video cameras require significantly higher bandwidth.
• Ease of use: Connecting devices to old ports is very inconvenient, especially through parallel port adapters. In addition, all ports are located on the back of the PC.
• Hardware resources: Each port requires its own IRQ line. The PC has only 16 IRQ lines, most of which are already occupied. Some PCs have only five free IRQ lines for connecting new devices.
• Limited number of ports: Many PCs have two serial COM ports and one parallel LPT port. It is possible to add more ports but at the cost of using valuable IRQ lines.

In recent years, I/O technology has become one of the most dynamic areas of desktop PC development, and two serial data standards have been developed that have greatly changed the way peripheral devices are connected and have taken the concept of plug and play to new heights. Thanks to the new standards, any user will be able to connect an almost unlimited number of devices to a PC in just a few seconds, without having any special technical knowledge.

Universal Serial Bus

Developed by Compaq, Digital, IBM, Intel, Microsoft, NEC and Northern Telecom universal serial bus(Universal Serial Bus - USB) provides a new connector to connect all common I/O devices, eliminating many of today's ports and connectors.

The USB bus allows connection of up to 127 devices using daisy chain connection(daisy-chaining) or use USB hub(USB hub). The hub itself, or hub, has several sockets and is inserted into a PC or other device. Each USB hub can connect seven peripheral devices. Among them there may be a second hub, to which seven more peripheral devices can be connected, etc. Along with the data signals, the USB bus also transmits the +5 V supply voltage, so small devices, such as hand-held scanners, may not have their own power supply.

The devices plug directly into the 4-pin socket on the PC or hub as a Type A rectangular socket. All cables that are permanently connected to the device have a Type A plug. Devices that use a separate cable have a Type B square socket, and the cable that connects them has a Type A or Type B plug.

The USB bus removes the speed limitations of UART-based serial ports. It operates at a speed of 12 Mb/s, which corresponds to network Ethernet technologies and Token Ring and provides sufficient bandwidth for all modern peripherals. For example, the USB bus has enough bandwidth to support devices such as external CD-ROM drives and tape drives, as well as ISDN interfaces regular phones. It is also sufficient to send digital audio signals directly to speakers equipped with digital-to-analog converters, eliminating the need for a sound card. However, the USB bus is not intended to replace networks. To achieve an acceptable low cost, the distance between devices is limited to 5 m. For slow devices such as keyboards and mice, the data transfer rate can be set to 1.5 Mbps, saving bandwidth for faster devices.

The USB bus fully supports Plug and Play technology. It eliminates the need to install expansion cards inside the PC and subsequently reconfigure the system. The bus allows you to connect, configure, use and, if necessary, disconnect peripheral devices while the PC and other devices are working. There is no need to install drivers, select serial and parallel ports, or define IRQ lines, DMA channels, and I/O addresses. All this is achieved by controlling peripheral devices using a host controller on the motherboard or on PCI card. The host controller and slave controllers in the hubs control peripheral devices, reducing processor load and improving overall system performance. The host controller itself is controlled by system software within the operating system.

Data is transmitted over a bidirectional channel controlled by the host controller and slave hub controllers. Improved bus mastering allows portions of the total bandwidth to be permanently reserved for specific peripherals; this method is called isochronous data transmission(isochronous data transfer). The USB bus interface contains two main modules: serial interface machine(Serial Interface Engine - SIE), responsible for the bus protocol, and root hub(Root Hub), used to expand the number of USB bus ports.

The USB bus allocates 500 mA to each port. Thanks to this, low-power devices that would normally require a separate AC adapter can be powered via cable - USB allows the PC to automatically detect the required power and deliver it to the device. Hubs accept full power from the USB bus (bus powered), but may have their own AC converter. Self-powered hubs delivering 500 mA per port provide maximum flexibility for future devices. Port switching hubs isolate all ports from each other, so one that is shorted does not disrupt the operation of the others.

The USB bus promises a PC with a single USB port instead of today's four or five different connectors. You can connect one large powerful device to it, such as a monitor or printer, which will act as a hub, providing connectivity to other smaller devices, such as a mouse, keyboard, modem, scanner, digital camera, etc. However, this will require the development of special device drivers. However, this PC configuration has disadvantages. Some experts believe that the USB architecture is quite complex, and the need to support many different types of peripheral devices requires the development of a whole set of protocols. Others believe that the hub principle simply shifts cost and complexity from the system unit to the keyboard or monitor. But the main obstacle to USB's success is the IEEE 1394 FireWire standard.

IEEE 1394 FireWire bus

This high-speed peripheral bus standard was developed by Apple Computer, Texas Instruments and Sony. It was designed as a complement to the USB bus, not as an alternative to it, since both buses can be used in the same system, similar to modern parallel and serial ports. However, large digital camera and printer manufacturers are more interested in the IEEE 1394 bus than the USB bus because digital cameras are better suited to the 1394 socket rather than the USB port.

IEEE 1394 (commonly called FireWire) is much like USB, also a hot-swappable serial bus, but much faster. IEEE 1394 has two interface layers: one for the bus on the computer's motherboard and one for the point-to-point interface between the peripheral device and the computer over a serial cable. A simple bridge connects these two levels. The bus interface supports data transfer rates of 12.5, 25 or 50 MB/s, and the cable interface supports 100, 200 and 400 MB/s, which is much faster than the USB bus speed of 1.5 MB/s or 12 MB/s. The 1394b specification defines other ways to encode and transmit data, allowing speeds to increase to 800 Mb/s, 1.6 Gb/s or more. Such high speed allows you to use IEEE 1394 to connect digital cameras, printers, TVs, network cards and external storage devices to a PC.

IEEE 1394 cable connectors are designed so that the electrical contacts are contained within the connector body, which prevents the possibility of electrical shock to the user and contamination of the contacts by the user's hands. These connectors are small and convenient, similar to the Nintendo GameBoy gaming connector, which has proven to have excellent durability. In addition, these connectors can be plugged blindly into the back of the PC. No terminal devices (terminators) or manual installation of identifiers are required.

The IEEE 1394 bus is designed for a 6-wire cable up to 4.5 m long, which contains two pairs of conductors for data transmission and one pair for powering the device. Each signal pair is shielded and the entire cable is also shielded. The cable allows voltages from 8V to 400V and currents up to 1.5A and maintains physical continuity of the device when the device is turned off or faulty (which is very important for a series topology). The cable provides power to devices connected to the bus. As the standard matures, the bus is expected to provide longer repeater-free distances and even greater throughput.

The basis of any IEEE 1394 connection is a physical layer chip and a communication layer chip, and the device requires two chips. The physical interface (PHY) of one device connects to the PHY of another device. It contains the circuits needed to perform the arbitration and initialization functions. The communication interface connects the PHY as well as the internal circuitry of the device. It transmits and receives packets in IEEE 1394 format and supports asynchronous or isochronous data transfers. The ability to support asynchronous and isochronous formats in the same interface allows non-time-critical applications such as scanners or printers, as well as real-time applications such as video and audio, to run on the bus. All physical layer chips use the same technology, while communication layer chips are specific to each device. This approach allows the IEEE 1394 bus to act as a peer-to-peer system, as opposed to the client-server approach of the USB bus. As a result, the IEEE 1394 system does not require either a serving host or a PC.

Asynchronous transfer is the traditional way of transferring data between computers and peripheral devices. Here, data is transmitted in one direction and is accompanied by subsequent confirmation to the source. Asynchronous data transfer emphasizes delivery rather than performance. Data transfer is guaranteed and retransmissions are supported. Isochronous data transfer streams data at a predetermined rate so that the application can process it based on timing. This is especially important for time-critical media data, where just-in-time delivery eliminates the need for expensive buffering. Isochronous data transfers work on the principle of broadcasting, where one or more devices can “listen” to the transmitted data. The IEEE 1394 bus can simultaneously transmit multiple channels (up to 63) of isochronous data. Since isochronous transfers can take up a maximum of 80% of the bus bandwidth, there is sufficient bandwidth left for additional asynchronous transfers.

IEEE 1394's scalable bus architecture and flexible topology make it ideal for connecting high-speed devices, from computers and hard drives to digital audio and video equipment. Devices can be connected in a daisy chain or tree topology. The figure on the left shows two separate work areas connected by an IEEE 1394 bus bridge. Work area #1 consists of a video camera, a PC and a VCR, which are all connected via IEEE 1394. The PC is also connected to a physically remote printer via a 1394 repeater, which increases the distance between the devices, amplifying bus signals. On an IEEE 1394 bus, up to 16 hops are allowed between any two devices. A 1394 splitter is used between the bridge and the printer to provide another port for connecting an IEEE 1394 bus bridge. Splitters provide users with greater topology flexibility.

Work area #2 contains only the PC and printer on bus segment 1394, as well as a connection to the bus bridge. The bridge isolates data traffic within each work area. IEEE 1394 bus bridges allow selected data to be transferred from one bus segment to another. Therefore, PC #2 can request images from the VCR in work area #1. Since the bus cable also carries power, the PHY signal interface is always powered and data is transferred even if PC #1 is turned off.

Each IEEE 1394 bus segment allows the connection of up to 63 devices. Now each device can be located at a distance of up to 4.5 m; long distances are possible both with and without repeaters. Cable improvements will allow devices to be carried over longer distances. Bridges can connect over 1,000 segments, providing significant expansion potential. Another advantage is the ability to perform transactions at different speeds on a single medium per device. For example, some devices can run at 100 Mbps, while others can run at 200 Mbps and 400 Mbps. Hot swapping (connecting or disconnecting devices) on the bus is allowed even when the bus is fully operational. Changes in the bus topology are automatically detected. This eliminates the need for address switches and other user interventions to reconfigure the bus.

Thanks to packet transfer technology, the IEEE 1394 bus can be organized as if memory space is distributed between devices, or as if the devices are in slots on the motherboard. The device address consists of 64 bits, with 10 bits allocated for the network ID, 6 bits for the node ID, and 48 bits for memory addresses. As a result, 1023 networks of 63 nodes can be addressed, each with 281 TB of memory. Addressing memory rather than channels treats resources as registers or memory that can be accessed using processor-memory transactions. All this provides a simple network organization; For example, digital camera can easily transfer images directly to a digital printer without an intermediary computer. The IEEE 1394 bus shows that the PC is losing its dominant role in connecting the environment and it can be considered a very intelligent node.

The need to use two chips instead of one makes IEEE 1394 peripherals more expensive than SCSI, IDE, or USB peripherals, making it unsuitable for slow devices. However, its benefits for high-speed applications such as digital video editing make IEEE 1394 the primary interface for consumer electronics.

Despite the advantages of the IEEE 1394 bus and the appearance in 2000 of motherboards with built-in controllers for this bus, the future success of FireWire is not guaranteed. The advent of the USB 2.0 specification greatly complicated the situation.

USB 2.0 specification

Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips took part in the development of this specification, aimed at supporting high-speed peripheral devices. In February 1999, performance improvements of 10 to 20 times were announced, and in September 1999, engineering studies raised estimates to 30 to 40 times over USB 1.1. Concerns have been expressed that with such performance, the USB bus will forever “bury” the IEEE 1394 bus. However, the general consensus is that these two buses are oriented towards various applications. The goal of USB 2.0 is to provide support for all current and future popular PC peripherals, while IEEE 1394 is aimed at connecting consumer audio and video devices such as digital video recorders, DVDs and digital televisions.

According to USB 2.0, throughput increases from 12 Mb/s to 360-480 Mb/s. USB 2.0 is expected to be compatible with USB 1.1, providing users with a seamless transition to the new bus. New high-speed peripheral devices will be developed for it, which will expand the range of PC applications. Speeds of 12 MB/s are sufficient for devices such as phones, digital cameras, keyboards, mice, digital joysticks, tape drives, floppy drives, digital speakers, scanners and printers. Increased throughput USB ability 2.0 will expand the functionality of peripheral devices, providing support for high-resolution cameras for video conferencing, as well as high-speed scanners and next-generation printers.

Existing USB peripherals will work unchanged in a USB 2.0 system. Devices such as keyboards and mice do not require the increased bandwidth of USB 2.0 and will function as USB 1.1 devices. The increased bandwidth of USB 2.0 will expand the range of peripheral devices that can be connected to a PC, and will also allow more USB devices to share the available bus bandwidth, up to the architectural limits of the USB bus. USB 2.0's backward compatibility with USB 1.1 could be a decisive advantage in the fight against the IEEE 1394 bus for the consumer device interface.

DeviceBay standard

Device Bay is a new standard that follows on from the IEEE 1394 and USB bus standards. These buses allow devices to be connected and disconnected on the fly, i.e. during the operation of the PC. Such opportunity hot swap(hot swap, hot plug) required a new one special connection between devices and the DeviceBay standard became the answer to this requirement. It standardizes bays into which hard drives, CD-ROM drives, and other devices can be inserted. The mounting frame is installed without tools and during PC operation. If the DeviceBay standard becomes widespread, it will do away with flat cables inside PC cases. The entire PC can be designed as a modular design, in which all modules are connected to USB or FireWire buses as DeviceBay devices. In this case, the device can be freely moved between the PC and other home devices.

The DeviceBay standard is designed to connect devices such as Zip drives, CD-ROM drives, tape drives, modems, hard drives, PC card readers, etc.

Buses, as you know, are used to transfer data from the central processor to other devices of a personal computer. In order to coordinate data transfer to individual components operating at their own frequency, a chipset is used - a set of controllers structurally combined into North and South bridges. The North Bridge is responsible for exchanging information with RAM and the video system, the South Bridge is responsible for the functioning of other devices connected through the appropriate connectors - hard drives, optical drives, as well as devices located on the motherboard (built-in audio system, network device, etc.), and for external devices – keyboard, mouse, etc.

The system board diagram is shown below.

To connect the processor with bridges, the FSB (Front Side Bus) bus is used (the most commonly used nowadays are Hyper-Transport and SCI), the north bridge (sometimes called the system controller) allows the most productive devices to function - the video adapter using the PCI Express 16x bus and RAM memory via the memory bus. The South Bridge ensures the operation of lower-speed devices connected using expansion cards (audio cards, network cards, video cards, etc.) via PCI buses and the PCI Express bus, optical drives and hard drives via ATA buses (formerly called IDE, now called PATA (Parallel ATA) and more modern SATA buses. Even slower devices are connected to south bridge via LPC bus – BIOS chip, a multicontroller for communication with external devices via serial and parallel ports - keyboard, mouse, printer, etc.

Note that in the most modern computers, the functions of the north bridge are performed by the central processor (Intel Nehalem, AMD Sledgehammer).

A computer has several buses through which data is transferred. The main one is the bus between central processor and North Bridge. You can read about the frequency of this bus in the section on processors. The next bus is between the processor and RAM (previously it was between the North Bridge and RAM). You can learn about its characteristics from the section on RAM. The buses that lead to expansion cards, which we will describe below, remain unexamined.

The data bus carries data directly, and the more lines it has, the more data can be transferred in one clock cycle, so the number of lines is constantly increasing. To transfer data inside the computer, a special bus is used, which consists of three parts, through which data, addresses, control signals, as well as grounding, voltage, etc. are transmitted. That is, practically data is transferred in three parts: address bus, data bus and bus management. The number of address bus lines determines the maximum address space where data can be sent, mainly to RAM. The 8086 processor had 20 address lines and could address 2 20 = 1 megabyte of memory, the 286 had 24 lines (2 24 = 16 megabytes), the 386 had 32 lines (2 32 = 4 gigabytes), modern computers have more than 32 lines. That is, the more lines in the address bus, the more RAM the motherboard supports.

The data bus transmits data directly and the more lines it has, the more data can be transferred in one clock cycle. Therefore, the number of lines is constantly increasing, starting from 8 in the first computers to 32 in Pentium systems.

Through the motherboard connectors, through the inserted cards, information is transmitted to/from the processor to external devices in relation to the motherboard. Naturally, these connectors cannot transmit more data than is supported by the internal system bus, and usually less, depending on the type of bus with which the expansion cards work. There are several types of buses and, accordingly, connectors: ISA, EISA, PCI and others. The latest computer models mainly use the more powerful PCI-E bus. But quite a few devices still run on less efficient buses. Therefore, modern motherboards have up to 5 different buses and their corresponding connectors.

Let's take a closer look at the available tires.

ISA bus(Industry Standard Architecture) appeared a long time ago and was a standard for a long time. Now it is hopelessly outdated. In total, the first XT models had 8 data lines, which allowed for byte transfer, 20 address lines for addressing up to 1 megabyte of memory, and another 34 lines for other purposes. When switching to the RS AT model, another 36 lines were added, including 8 for data and 4 for address. 8-bit was used in PC XT, had 62 contacts and allowed addressing 1 MB of memory. Next came the 16-bit (sometimes called AT BUS), operating at a frequency of 8 MHz with a speed of 16 Mb/sec, allowing you to address up to 16 Megabytes. It consists of two parts, the first of which corresponds to the 8-bit ISA bus slot. An additional 8 bits are used for additional addresses I/O and contain 36 connectors (so you can install 8-bit cards in a 16-bit slot). However, this device had a clock frequency of 8.33 MHz and worked slowly, so other buses appeared.

Currently, the Plug-an d-Play (PnP) standard works, which allows configuration to be performed automatically when installing a new device. In this case, the system itself determines the type of device, I/O port address, interrupt number and direct memory access (DMA) channel. However, older tires have difficulty using this standard. Thus, the ISA bus was developed before the advent of PnP. Therefore, not all devices that connect to this bus can be automatically configured. To exit current situation Windows 9x has a list of devices that can be connected to the computer and which install themselves.

The ISA bus has the following restrictions:

The presence of a 16-bit bus, that is, the ability to simultaneously send two bytes;

Maximum clock frequency 8.33 MHz;

No sharing of interrupts and DMA channels across multiple cards in different slots;

Inability to programmatically disable the card in the event of a device conflict;

Lack of software control of I/O port addresses, interrupt lines and direct access channels.

To install an ISA card on an EISA bus, you typically need to have a configuration file to run the EISA bus configuration utility, which will then allocate resources to the card.

When installing a new device, you need it to be physically and logically compatible. Physical alignment means that the type of connector and the number of pins on the plug and connector must match each other. Logical alignment means that the contacts through which voltage is supplied, where there is grounding, etc. must be clearly defined. In this case, the signal sent over one contact must be identified by the receiving device as a data transfer signal, and not as a control signal. All this is determined by the tire standard.

This standard is usually established by the manufacturer, which has begun mass production of new devices. These include the EIDE bus for connecting hard drives, serial and parallel ports, a bus for outputting graphic images, a bus for connecting expansion cards, a USB bus, IrDA, etc., which have their own standards. However, in practice, the term bus often refers to the bus to which the expansion card is connected. Therefore, in this book, from now on, the bus will simply be called the PCI bus, VESA bus, etc. In conclusion, we note that the first computer buses were called Multibus1. They were produced in two versions: PC/XT bus and PC/AT bus and had 7 lines for hardware interrupts. They were later replaced by the ISA bus.

MCA bus(Microchannel) appeared in 1987, developed by IBM and installed on the PS/2 ISA computer. There are two types: 16-bit and 32-bit. The 32-bit operates at a frequency of 10 MHz, with a data transfer rate of up to 20 Mb/s, and allows you to address up to 4 gigabytes. The expansion card could be independently recognized and automatically configured by the computer. The main disadvantage is the incompatibility with the ISA bus, for which the main devices were developed, so this architecture is not widely used.

TireEISA(Extended ISA - extended ISA) was released by a group of companies competing with IBM in 1988, since the MCA bus had closed description and it could only be used by IBM, and is also already outdated. The advantages include its compatibility with the ISA connector due to the arrangement of the connectors in two layers, on one ISA, on the second - EISA. This bus is 32-bit, operates at a frequency of 8.33 MHz and provides a maximum data transfer speed of up to 33 Mb/s. The configuration is set programmatically, not using switches.

To prevent the two layers from being shorted when installing a card that requires an ISA connector, the connector has a plug that prevents connection to the bottom contacts. The EISA card contains a cutout in the place of the plug that allows you to bypass this plug.

Due to its high cost, the EISA bus was not widely used in personal computers, but was used in workstations and servers.

Tire SCSI(Small Computer System Interface - small system computer interface) is designed to connect large arrays of devices to the bus, such as hard drives, optical drives, streamers, printers, etc. Therefore, it is mainly used in server computers or computers with a RAID system. It is practically not used in home computers.

SCSI-1 appeared in 1986, had 8 data lines, each device with its own number, with the adapter assigned number 7. The remaining devices have a number from 0 to 6, and the number is set manually on the back of the connected device or using jumpers. Devices on the bus can exchange information with each other without the participation of an adapter, which in this case determines who can transfer data to whom. At the same time, when information passes through him, he takes part in it. Bus frequency is 5 MHz, maximum number of connected devices is 8.

Fast SCSI appeared in 1991 and had 8 data lines, as well as an improved cable connector. Bus frequency – 10 MHz, bandwidth – 10 MB/sec, maximum number of connected devices – 8.

Wide SCSI had 16 lines for data transmission, bus frequency – 10 MHz, bandwidth – 20 MB/sec, maximum number of connected devices – 16.

Ultra SCSI appeared in 1992, had 8 lines for data transmission, bus frequency - 20 MHz, bandwidth - 20 MB/sec, maximum number of connected devices - 4-8.

Ultra Wide SCSI had 16 lines for data transmission, bus frequency - 20 MHz, bandwidth - 40 MB/sec, maximum number of connected devices - 4 - 16.

Ultra 2 SCSI appeared in 1997, had 8 lines for data transmission, bus frequency – 10 MHz, bandwidth – 40 MB/sec, maximum number of connected devices – 8.

Ultra 2 Wide SCSI had 16 lines for data transmission, bus frequency – 40 MHz, bandwidth – 80 MB/sec, maximum number of connected devices – 16.

Ultra 3 SCSI had 16 lines for data transmission, bus frequency – 40 MHz, bandwidth – 160 MB/sec, maximum number of connected devices – 16.

Ultra -320 SCSI had 16 lines for data transmission, bus frequency – 80 MHz, bandwidth – 320 MB/sec, maximum number of connected devices – 16.

Ultra -640 SCSI appeared in 2003, had 16 lines for data transmission, bus frequency – 160 MHz, bandwidth – 640 MB/sec, maximum number of connected devices – 16.

Subsequently, technology began to develop SAS(Serial Attached SCSI) for working with hard drives and tape drives. You can connect SATA devices to a SAS connector, but not vice versa. Provides throughput of 1.5, 3.0, 6.0 Gbit/s, 12 Gbit/s expected. Allows you to connect not only 3.5-inch drives, but also 2.5-inch drives.

The adapter itself is located on the motherboard (like a Mac) or on an expansion card. The card is inserted into the PCI slot. The SCSI device cable on Mac computers has a female connector with a DB25 connector, the same as the parallel port. If you accidentally connect it to a printer or parallel port on a computer, or, conversely, connect a printer cable to a SCSI device, the chips of the device to which they are connected may burn out.

When transmitting data over a cable, a so-called “standing wave” may arise in it. To prevent it from happening, a special plug is used to extinguish it. Moreover, this plug should be one and located at the end of the cable. SCSI devices can have two connectors, one of which is connected to the SCSI bus, and the second, if it is at the end of the cable, must have a plug. If there are two stubs on two devices on a line, they may prevent each other from performing their role.

The SCSI bus works with hard drives somewhat differently than other standards, considering the disk not as records having heads, cylinders, sectors, but as a sequence of logical records. When the SCSI adapter receives information from the CPU for the hard drive about a record at a specific address, it translates it into a logical record number. As a result, if HDD put in place of any SCSI device of this adapter, it will work, but if installed in other adapters, the system may not read the data about converting the disk to the new structure, all information on the disk will be destroyed.

Other devices (optical drives, Iomega) have special drivers, in which you can freely move them from one system to another. You can use both devices connected to a SCSI adapter and EIDE at the same time on one computer.

SCSI devices require a termination at the end of the cable that connects them. As a rule, it is installed at the factory on each device. Therefore, when installing all devices except the last one, you need to remove them. If devices connected to the SCSI bus do not support the Plug & Play standard, then the device number must be set on them using jumpers. Keep in mind that some adapters require devices numbered 0 and 1 to be hard drives.

EIDE bus intended for connecting hard drives and optical drives. Also called as ATA or RATA(parallel ATA). Now it is being replaced by the SATA bus, but, nevertheless, it is also installed on modern boards, since several optical drives can be connected to it (two for each connector). This is discussed in more detail in the section on hard drives. The first disk drives were connected to the computer using cards that contained a disk controller. Over time, as chip sizes decreased, the controller began to be installed on the hard drive, and the floppy drive controller on the motherboard, so it became possible to connect hard drives directly through the connector on the motherboard.

This is how the IDE bus appeared, which is part of the ISA bus, which is connected to a special connector (in modern devices there are two connectors) on the motherboard. First, a bus standard called ATA was developed, then ATAPI, which made it possible to work with optical drives. Over time, an expanded version of EIDE appeared with the ATA standard and subsequently an extension of the standard - ATAPI. If there are more devices connected to the EIDE connector than the computer can support, then you need to install a special card to which you can connect several more devices.

The first standards used hard drives connected to the board using special cards on which the controller was located, to the ISA bus. Over time, sizes electronic components were reduced and they began to be installed on the hard drive itself. Next, drives began to be connected to the board via an IDE connector, then two connectors appeared, and up to two devices could be connected to each connector, performance increased, addressing of logical blocks was introduced, it became possible to connect optical drives, and all this was supported by the EIDE standard, which works with a clock frequency of 8.33 MHz. The first devices worked with the ATA standard, and then ATAPI, which made it possible to connect to a channel optical device. Since it became possible to transmit 2 bytes simultaneously over the channel in one clock cycle, the transfer speed over the same lines reached 16.6 MB/sec. Over time, data was transferred in one clock cycle not only when moving from high to low voltage, but also when moving from low to high. This standard is called Ultra ATA or ATA33, as it allows data transfer at a speed of 33.3 MB/sec.

Later, the ATA66 standard appeared, in which the clock frequency in the channel increased to 16.7 MHz and data transfer occurs at a speed of 66.7 MB/sec. Cable for connecting hard The drive to the motherboard is different and contains 80 wires instead of 40, as was the case with previous standards. There are 40 wires used to connect devices to this cable. If you connect a device capable of operating in ATA33 to this channel, or a device operating with the ATA66 standard to the ATA33 bus, the device will operate at a speed of 33.3 MB/sec. In some boards, ATA and its extension ATAPI allows you to connect devices with different speeds to the same bus without reducing performance, but it is better to separate them into different channels.

The cable for working with the IDE ATA (AT-Bus) standard is 16-bit, has 40 cores. The XT IDE cable (8 bit) also has 40 cores, but is not ATA compatible, meaning it cannot be used for the IDE standard.

There are two DMA channel operating modes: Singleword and Multiword. Singleword DMA has mode 0, which operates at a speed of 2.08 MB/sec, mode 1 – 4.16, mode 2 – 8.33, and Multiword DMA has mode 0, which operates at a speed of 4.12, mode 1 – 13.3, mode 2 – 16.6 MB/sec . Ultra DMA mode has mode 0, operating at speed – 16.6, mode 1 – 25, 2 – 33.

In addition, there are other PIO modes, from 0 and higher, and the higher the number, the faster the bus runs.

ATA-2 mode operates in PIO Mode 3 multiword DMA Mode 1, supports LBA and CHS. Fast ATA-2 supports Multiword DMA mode 2 and PIO mode 4. ATA3 is an extension of ATA2 with Smart, that is, it improves power consumption. ATA/ATAPI-4 - extension of ATA3, has Ultra DMA, ATAPI interface. E-IDE supports PIO mode3, with multiword DMA mode 1 and works with LBA and CHS. Ultra DMA requires an 80-conductor cable with 40-pin shielded connectors. The IDE Mastering standard allows an external device to control the system bus for data transfer without controlling the processor bus, but using such a bus eliminates DMA channel allocation problems and capacity limitations. In particular, it works with 8- or 16-bit data. Next came the operating modes ATA-3 (another name for EIDE), ATA-4 (frequency 16.7, 25, 33.3, another name for Ultra ATA /33), ATA-5 (frequency 66 MHz, another name Ultra ATA /66), ATA-6 (frequency 100 MHz, another name Ultra DMA 100 or UDMA 5 (100)), ATA-7 (frequency 133 MHz, another name Ultra DMA 133 or UDMA 6 (133)), ATA-8 (in development).

Tire VESA(Video Electronics Standard's Association - Association of Video Electronic Standards or VL-BUS or VLB or VESA local bus) was outdated, first appeared after the ISA bus and had four times the speed of ISA, but it had some limitations, in particular, it was possible have only 2-3 connectors, which undoubtedly reduced the computer's capabilities. It is a bus for connecting a display, but can be used for other devices; it is not an extension of the ISA bus (like previous buses). This card is directly connected to the CPU bus, bypassing the system bus. Works with system bus frequencies up to 66 MHz, used mainly with 486, sometimes with 386 computers for video cards and hard drives. A new version 2.0 was released for the Pentium, but it was not widely used and is currently practically not used.

PCI bus(Peripheral Component Interconnect - connection of peripheral components) is also not based on the ISA bus and is a completely independent, synchronous bus, developed by Intel, the first versions operated at a frequency of 33 MHz, had a 32-bit (or 64-bit) channel and is independent of central processor, that is, it allows you to transfer data while the processor is busy with other calculations. The theoretical bus throughput was 133 MB/sec, but in reality it was 80 MB/sec. This tire is still widely used today.

The PCI bus began to be developed at the same time as the ISA bus, but was completed later. The PCI bus has more data transfer lanes than ISA, and it works faster than ISA, and total number There are 124 contacts in the connector. The bus allows you to detect errors during data transmission and operates without a cable plug. In addition, during installation it allows you to configure the connected device, that is, the computer reads information from the device’s memory, where its main parameters are stored. The tire can work not only with a certain set chips on the motherboard, but also with different devices, as well as in other types of computers. In addition, the PCI bus is capable of sharing interrupts and DMA channels between different devices, which was the impetus for its active implementation, while the ISA bus could not provide this.

You can connect cards to the PCI bus connector: those with power supply: 5 V (key 50, 51 pins), 3.3 V (key 12, 13) and universal (key 12, 13, 50, 51 pins). A 32-bit slot has 62 contacts on each side, a 64-bit slot has 94. This bus allows you to connect up to four devices simultaneously, that is, it can have up to four connectors. For use more connected devices, a special microcircuit is used - a bus bridge, to connect two buses. For industrial devices there is a Compact PCI standard with 8 slots.

While the PCI bus was being developed, other industries were also developing. The clock frequency of the internal bus has increased to 100, 150 and higher MHz, the number of data lines has increased to 64 and continues to increase, however, the type of PCI bus remains 32-bit, but in the future the PCI bus will also develop.

Each slot has 256 eight-bit registers that contain configuration parameters. After turning on the computer's power, a request is made to configure the bus during the execution of the Post program; after setting the parameters, the bus can perform I/O operations. The main advantage of the bus is that data transfer occurs without the involvement of the central processor, that is, while data is being transferred from one device to another, the central processor can carry out its tasks.

The PCI 1.0 bus is 32-bit with a bandwidth of 132 MB/s, addressing up to 4 gigabytes, and PCI 2.0 is 64-bit with a bandwidth of 528 MB/s. This bus is adapted for Plug&Play technology, that is, the boards are configured by software. For industrial applications, the Compact PCI standard is used, in which up to eight devices can be installed simultaneously.

Interrupt conflict resolution on the PCI bus is achieved by allowing the bus to handle processing for each device in turn. The PCI bus provides 32 data lines at a clock frequency of 33 MHz, then became 64-bit, with a clock frequency of 66 MHz, and the new version of the bus can accommodate old PCI cards, as well as a new card in the old slot. Newer versions of PCI can increase the clock speed and allow you to use old expansion cards to run them, as well as install new cards in old slots.

AGP bus(Accelerated Graphics Port) was developed by Intel in 1997 specifically for working with a video card, at a frequency of 66 MHz it has a 32-bit data bus. Currently supplanted by the PCI-E bus. The bus allows you to use pipelining of requests, that is, sending data in the form of continuous packets. In the PCI bus, the previous data and the address for the next data are sent, after which time delays occur, and in the AGP bus, several addresses and several data are sent one after another, which reduces the delay. It is possible to queue up to 256 requests and maintain two queues for high and low priority read/write operations. Dual transmission, that is, the transmission of two data in one clock cycle instead of one, allows you to have a throughput at a frequency of 66 MHz up to 528 MB/sec. Allows operation at frequencies up to 100 MHz and higher with higher throughput. Quad transfer allows you to transfer up to 1,056 MB/sec.

There are several standards for the AGP bus: AGP 1X, 2X, 4X, Pro and 8X. Most cards work with the 4X and 8X standard. RAM stores not only parts of the image, but also graphic textures. To ensure that the video system can only access those areas of memory that concern it, a special GART table (Graphics Address Remapping Table) is used to define these memory areas.

The bus has the ability for the video processor to directly access areas of RAM, as well as video memory, and process textures there in DiMe (Direct Memory Execution) mode, while the addressing is the same. The bus is used for Pentium Pro, Pentium II, Pentium III and Pentium IV processors, but can also work with Pentium processors.

SATA(Serial ATA) is a development of the IDE interface. Its feature is not parallel data transmission, but serial one, which, although slower, allows the use of higher frequencies without the need for signal synchronization. The first SATA 1.x standard could operate at 1.5 GHz with a throughput of 1.2 Gbps (transmission loss large quantity service information). The 2.x standard operates at a frequency of 3 GHz with a throughput of up to 2.4 Gbit/s and the 3.0 standard at a frequency of 6.0 Gbit/s, with a throughput of 4.8 Gbit/s.

To connect devices inside the system unit, they are connected to the 7-pin SATA information connector on the motherboard and a 15-pin power cable to the power supply. There are devices that allow you to connect both a 15-pin cable and a 4-pin Molex electrical power cable. Please be aware that connecting two cables at the same time may burn out the device.

There are adapters from SATA to IDE and vice versa.

eSATA(External SATA - external SATA) is designed for connecting devices in hot-swappable mode, that is, when the computer is turned on. In order to be able to do this in Windows XP, you need to install the AHCI driver. Was created in 2004. Has a connector similar to SATA, but has added connector shielding. Therefore, it is not compatible with the SATA connector, since they are electrically compatible, but not physically. The cable length has been increased to 2 meters (1 meter for SATA).

There is a combined eSATA + USB connector = Power eSATA, which has not only information lines, but also power lines.

PCI - E(or PCI Express or PCI-E) appeared in 2002, uses a star-type connection between devices, allowing hot-swapping of devices. There are several options x1, x2, x4, x8, x12, x16, x32, which have different connectors. The lower the number, the fewer pins and shorter the connector length. Devices that are designed for x8 connector can be connected to connectors with a larger number, in in this case, x12, x16, x32. This rule applies to other species.

There are three standards. Standard 1.0 allows you to transfer in one direction for x1 - 2 Gbit/s, in two directions - 4 Gbit for x1. The throughput of other types can be calculated by multiplying the above figure by the number in the name. For example, for x16 the throughput in one direction is 2 x 16 = 32 Gbit/s. Standard 2.0 was released in 2007, has a throughput in one direction (double in two directions) for x1 - 4 Gbit/s. You can also calculate throughput for other species. Standard 3.0 released in 2010, it allows you to transfer data at a speed of 8 Gbit/sec. Standard 4.0 is scheduled to be released by 2015 and will be twice as fast as 3.0.

Currently, the most common on motherboards are x16 for connecting video cards and x2 for connecting other devices.

USB bus(Universal Serial Bus - universal serial bus) is designed for connecting peripheral devices (for example, keyboard, mouse, joystick, printer and others). Its mission is to connect various devices to a running computer, for example, toasters, keyboards, microwave ovens, LED lights, fans, etc., without the need to install switches, jumpers, use software (drivers), etc. for this.

First standard 1.0 appeared in 1994 and has a mode with low throughput of 1.5 Mbit/s (Low speed), with high throughput (Full-speed) up to 12 Mbit/s. The USB bus can operate in two modes: low-speed, in which the keyboard, mouse, etc. operates, with a low transmission speed (cable length - 5 meters) and high-speed mode (cable length - 3 meters), which allows you to work with maximum printer speed.

In version 1.1, existing errors were corrected.

Standard 2.0 a new mode has appeared (Hi-speed) with a throughput of 25480 Mbit/s.

You can connect devices on this bus, and the computer itself will determine the device that is connected. In this case, it is possible not only to connect a new device directly to the computer, but also to a device that is already connected to the computer. For example, you can connect a hard drive, microphone and other devices to the keyboard.

It can use a hub to which you can connect up to 127 devices and supports Plug&Play technology. In this case, the bus automatically assigns a number to the devices with which it operates. In addition to sending data, these wires also transmit electricity, but in a small amount, which is enough for the keyboard, but may not be enough for the speakers. Therefore, speakers with high output power require a separate power supply.

The bus allows you to connect devices when the computer is turned on. When connected, they request a host device, which assigns them addresses, after which they can begin to work. In addition to data, electricity is also transmitted, which is used to power devices. If there is not enough electricity, the devices can be connected to an additional power source.

In addition to increasing computer performance, the need for upgrading may arise when adding new devices, which requires the appropriate power supply power, a certain number and type of connectors for expansion cards on the motherboard and the number of free compartments inside the system unit. Over time, with the spread of the USB standard, many devices that can now be connected are not located inside, but rather brought outside the system unit. Thus, more and more external devices will be produced and the number of connectors inside the case and compartments will not be a problem when installing a large number of additional devices.

Latest standard USB 3.0 appeared in 2008, connectors are compatible with earlier standards. However, four more communication lines were added in the form of two twisted pairs and the cable itself became thicker. The connectors on the motherboard for connecting such cables are blue, and the plugs themselves have blue inserts. Thus it was raised maximum speed data transfer up to 4.8 Gbit per second, and the transfer speed increased to 600 MB per second (higher than the standard USB 2.0 ten times). At the same time, the transmitted current has increased from 500 mA to 900 mA, which allows you to connect more energy-intensive devices.

Tire PCMCIA used in laptops and has the ability to transmit data over 16 bits with addressing up to 64 Megabytes, with a bus frequency of 33 megahertz. This bus allows you to connect different devices - hard drives, modems, memory expanders, etc. Many adapters are produced using PnP technology and have the ability to connect devices without turning off the computer. All devices connected to this connector have reduced power consumption. The bus has great prospects in the future and will be installed in desktop computers.

PCMCIA cards, also called PC cards, are designed for RAM, modems, hard drives, and other devices and come in three types. They have a length and width of 85x54 mm, and the thickness depends on the type. Type I has a thickness of 3.3 mm, type II - 5 mm, type III - 10.5 mm. The card is inserted into a slot on the ISA bus designed for these cards, also called PCMCIA.

Type I is used for RAM, sometimes for modems or a network card, has a 16-bit interface, thickness 3.3 mm, type II is for the same devices, but they are thicker (5 mm), type III can also install a hard drive (thickness 10. 5 mm). The laptop has a compartment where you can install either one type I or II card, or in modern models - two cards of type I and II or one type III.

For the modem, at the end of the card there is a special connector (X-jack) to which the wire is connected; at the other end there is a telephone connector (RG11) for connecting to a telephone line. When installing, you just need to insert the card into the hole until it clicks, and in order to remove it, you need to press the adjacent key, and the card will pop out. PC Card AT is a PCMCIA connector for connecting to notebook and desktop computers.

Card Bus is a further development of PC Cards, which transmit data via a 32-bit interface (PCMCIA cards became known as PC Cards). The bus connects the card to the video system, allowing it to bypass the ISA bus. This bus is called Zoomed Video Port - enlarged video port.

IEEE 1394– developed by the Institute of Electrical and Electronics Engineers (IEEE) based on the Apple bus – FireWire in 1995, where the number 1394 indicates the serial number of the tire that was developed by this organization. The bus allows you to connect up to 16 devices to one node, and each device is assigned a number, which is 16 bits in size, that is, more than 64,000 devices can be addressed in total. Up to 63 devices are connected to each bus, and each node is assigned a number consisting of 6 bits. 1023 buses can be connected to each other using bridges, each of which has a capacity of 10 bits; the bus can be “hot-swappable”. Each new device can be connected to any free port; on one device there are from one to three of them, but up to 27 are possible. The only exception is the prohibition of organizing loops of devices, since the bus supports a tree structure.

There are three classes of devices with 98.3 data transmission; 196.6 and 339.2 Mbps, or they are usually rounded up to 100, 200 and 400 Mbps according to the IEEE 1394a standard and 800 and 1600 according to the IEEE 1394b standard. According to the IEEE 1394.1 standard, developed in 2004, you can connect up to 64,449 devices; according to the IEEE 1394c standard, developed in 2006, you can use an Ethernet cable. In this case, the maximum cable length is up to 100 meters, and the speed is up to 800 Mbit/s.

There are three types of connectors: 4 pin – without power, installed on laptops and video cameras (IEEE 1394a without power), 6 pin – with additional two contacts for power(IEEE 1394a) and 9 pin with additional contacts for reception and transmission(IEEE 1394 b). There may also be an RJ-45 connector(IEEE 1394c) .

If the cable consists of 6 copper wires, two for power, the remaining two pairs for data, each pair is shielded and all wires together are also shielded. Since a power supply of 8 to 40 volts is provided at a current of up to 1.5 amperes, many devices do not require additional connection to the network. Cables up to 4.5 meters can be installed between two devices, bus connectors are simple, with possibility of easy connections.

The bus operates in synchronous and asynchronous modes. Asynchronous transmission sends data organized in packets and repeats the transmission if errors occur, which is important for accurate data transfer. Synchronous transmission is used in multimedia to transmit audio and video data, but if the data is lost, this is not critical, since the next portion of data is transmitted.

The IEEE 1394 bus transmits data digitally, so the video image quality is better than analog. The computer can programmatically turn on and off devices connected to it. The bus is independent of the computer, that is, it can operate in the absence of a computer, for example, to transfer data from a video camera to a VCR. This bus is supported by Windows 98 (update required), Windows ME, Windows 2000, Windows XP and others.

To speed up work, it was introduced host bus(sometimes called the processor bus). Designed to transfer 64-bit data between the processor, RAM and L2 cache and operates at 50, 60, 66, 75, 100, 133 MHz, while the PCI bus operates at half the frequency (25 ; 30; 33; 37.5 MHz).

Exploitation. If one of the old cards stops working, you can try to remove it and clean the contacts with an ordinary eraser, which will remove deposits and oxide. After installation, check the operation of the board. It is advisable to cover unused slots with special covers.

SYSTEM BUS SYSTEM BUS

SYSTEM BUS (system bus), a set of lines for transmitting all types of signals (including data, addresses and control) between the microprocessor (cm. MICROPROCESSOR) and other electronic devices of the computer (cm. COMPUTER). The part of the system bus that transmits data is called the data bus, addresses are called the address bus, and control signals are called the control bus. Important characteristic The system bus that affects the performance of a personal computer is the clock frequency of the system bus - FSB (Frequency System Bus).
A personal computer based on an x86-compatible microprocessor is built according to the following scheme: the microprocessor is connected to a system controller via the system bus (usually such a controller is called a “North Bridge”). The system controller includes a RAM controller and bus controllers to which peripheral devices are connected. The most powerful peripheral devices (for example, video cards) are usually connected to the north bridge (cm. VIDEO ADAPTER)), and less productive devices (BIOS chip, devices with a PCI bus) are connected to the “South Bridge”, which is connected to the North Bridge by a special high-performance bus. A set of “south” and “north” bridges is called a chipset (cm. CHIPSET)(chipset). The system bus acts as a backbone between the processor and the chipset.

encyclopedic Dictionary. 2009 .

See what "SYSTEM BUS" is in other dictionaries:

system bus- backbone of the PC system unit - [E.S. Alekseev, A.A. Myachev. English-Russian explanatory dictionary on computer systems engineering. Moscow 1993] Topics information technology in general Synonyms backbone of the PC system unit EN system busS bus ...

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input/output channel bus (computer)- Local system bus of the processor, usually used as an input/output channel for the motherboard of a single-processor computer, for example, in IBM PC XT, Apple Mac II, DEC Professional 325/350/380. [E.S. Alekseev, A.A. Myachev. English Russian... ... Technical Translator's Guide

AGP connector on the motherboard (usually brown or green flowers). AGP (from the English Accelerated Graphics Port, accelerated graphics port) is a system bus for a video card developed by the company in 1997. Appeared simultaneously with chipsets... Wikipedia

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FSB (English Front side bus, translated as “system bus”) is a computer bus that provides a connection between an x86 compatible central processor and the outside world. As a rule, a modern personal computer based on x86 compatible... ... Wikipedia