Internal and external memory storage devices. Types of memory storage devices. External memory devices - computer hardware - ICT hardware and software - catalog of articles - computer science textbook

Barnaul 2005

Introduction 3

1. External memory 5

2. hard drives 8

3. RAID 11 disk arrays

4. CDs 13

5. Practical part 17

Conclusion 26

References 27

Introduction

External computer memory usually means both storage media (that is, devices where it is directly stored) and devices for reading/writing information, which are most often called drives.

As a rule, each storage medium has its own storage device.

The first storage media for computers were paper (punched cards, punched tapes). To work with them, there were 2 separate devices: a puncher - for recording information, a counter - for reading information and transferring it to RAM. Later, magnetic storage media (magnetic tapes, magnetic drums, magnetic disks) appeared, the drives of which combined both a reading device and a recording device. A device such as a hard drive combines both a storage medium and a storage device. For optical storage media (CDs, digital discs), drives can either combine read/write functions or be specialized, for example, read-only.

Hard magnetic disk drives (HDDs or hard drives) are external storage devices in which the storage medium is hard, non-removable magnetic disks combined into a package.

HDDs are designed for long-term storage of information constantly used when working with a PC: operating system programs, frequently used software packages, document editors, translators from programming languages, documents and programs prepared by the user, etc.

Currently, PCs without HDD are practically not produced. If the computer is included in a local computer network, then it can work without its own hard drive, but then it uses the hard drive of the central server.

The hard drive is installed inside the system unit and externally is a sealed metal box, inside of which there are several disks combined into one package, magnetic read/write heads, a mechanism for rotating the disk and moving the heads.

The main characteristics of the hard drive are:

Capacity, that is, the maximum amount of data that can be written to the medium;

Performance, determined by the time of access to the necessary information, the time of reading/writing it and the data transfer rate;

Uptime, which characterizes the reliability of the device.

The HDD capacity depends on the PC model. The first hard drive (early 80s) had a “colossal capacity” of 10 MB. It is believed that the volume of a modern hard drive should be at least 2–3 GB. The latest PC models have hard drives with a capacity of over 120 GB, and hard drives with a capacity of up to 320 GB are expected to appear.

Most often, the hard drive is named C:. However, the capacity of a hard drive is usually very large, so for ease of operation the hard drive is divided into sections. Each such section is perceived by the operating system as a separate disk and is called a “logical disk”. The names of such disks are C:, D:, E:, etc. in alphabetical order.

EXTERNAL MEMORY

External memory devices or, otherwise, external storage devices are very diverse. They can be classified according to a number of characteristics: by type of media, type of design, principle of recording and reading information, access method, etc.

A medium is a material object capable of storing information.

Depending on the type of media, all VSDs can be divided into magnetic tape drives and disk drives.

Magnetic tape drives, in turn, come in two types: reel-to-reel magnetic tape drives (NBML) and cassette tape drives (NCM streamers). PCs use only streamers.

Disks are classified as direct access storage media. The concept of direct access means that the PC can “access” the track on which the section with the required information begins or where new information needs to be written, directly, wherever the drive’s write/read head is located.

Disk drives are more diverse

floppy magnetic disk drives (FMD), otherwise known as floppy disks or floppy disks; hard magnetic disk drives (HDD) of the Winchester type; drives on removable hard magnetic disks using the Bernoulli effect; drives on floptic disks, otherwise, floptical drives; ultra-high density drives, otherwise known as VHD drives; optical CD drives CD-ROM (Compact Disk ROM); optical disk drives of the CC WORM type (Continuous Composite Write Once Read Many - write once - read many times); magneto-optical disk drives (NMOD), etc.

Accumulation type	Capacity, MB	Access time, ms	Transfer, KB/s	Type of access
				Read/Write
Winchester				Read/Write
Bernoulli				Read/Write
				Read/Write
				Read/Write
				Only reading
				Read/write once
				Read/Write

Note Access time - the average time interval during which the drive finds the required data - is the sum of the time for positioning the read/write heads on the desired track and waiting for the desired sector. Transfer - data transfer speed during sequential reading.

Magnetic disks (MD) refer to magnetic computer storage media. As a storage medium, they use magnetic materials with special properties (with a rectangular hysteresis loop) that make it possible to record two magnetic states - two directions of magnetization. Each of these states is associated with binary digits: 0 and 1. Memory media (MD) are the most common external storage devices in PCs. Disks are hard and flexible, removable and built into the PC. A device for reading and writing information on a magnetic disk is called a disk drive.

All disks: both magnetic and optical, are characterized by their diameter or, in other words, form factor. The most common drives are with form factors of 3.5" (89 mm) and 5.25" (133 mm). Disks with a 3.5" form factor with smaller dimensions have higher capacity, shorter access time and higher speed of reading data in a row (transfer), higher reliability and durability.

Information on the MD is written and read by magnetic heads along concentric circles - tracks (tracks). The number of tracks on an MD and their information capacity depend on the type of MD, the design of the MD drive, the quality of the magnetic heads and the magnetic coating.

Each MD track is divided into sectors. One track sector can hold 128, 256, 512, or 1024 bytes, but typically 512 bytes of data. Data exchange between the NMD and the OP is carried out sequentially by an integer number of sectors. A cluster is a minimal unit of information placement on a disk, consisting of one or more adjacent track sectors.

2. Hard drives

Winchester-type drives are widely used in PCs as hard magnetic disk drives (HDDs).

The term hard drive arose from the slang name for the first model of hard drive with a capacity of 16 KB (IBM, 1973), which had 30 tracks of 30 sectors, which coincidentally coincided with the “30/30” caliber of the famous Winchester hunting rifle.

In these drives, one or more hard drives made of aluminum alloys or ceramics and coated with ferrolacquer, together with a block of magnetic read/write heads, are placed in a hermetically sealed housing. The capacity of these drives, thanks to the extremely dense recording obtained in such non-removable designs, reaches several thousand megabytes; Their performance is also much higher than that of NGMD.

Maximum values for 1995:

capacity 5000 MB (capacity standard for 1995 is 850 MB); rotation speed 7200 rpm; access time - 6 ms; transfer - 11 MB/s. HDDs are very diverse. The drive diameter is most often 3.5" (89 mm), but there are others, in particular 5.25" (133 mm) and 1.8" (45 mm). The most common drive housing height is 25 mm for desktop PCs, 41 mm - for server machines, 12 mm - for laptop PCs, etc.

Modern hard drives began to use the zone recording method. In this case, the entire disk space is divided into several zones, and the outer zones of the sectors contain more data than the inner ones. This, in particular, made it possible to increase the capacity of hard drives by approximately 30%.

In order to obtain a disk structure on a magnetic medium, including tracks and sectors, a procedure called physical, or low-level formatting, must be performed on it. During this procedure, the controller writes service information to the media, which determines the layout of the disk cylinders into sectors and numbers them. Low-level formatting also involves marking defective sectors to prevent access to them during the operation of the disk.

The maximum capacity and data transfer speed depend significantly on the interface used by the drive.

The now widespread AT Attachment (ATA) interface, widely known under the name Integrated Device Electronics (IDE), offered in 1988 to IBM PC/AT PC users, limits the capacity of one drive to 504 MB (this capacity is limited by the address space of traditional head-to-cylinder addressing - sector": 16 heads * 1024 cylinders * 63 sectors * 512 bytes per sector = 504 KB = 528,482,304 bytes) and provides a data transfer rate of 5-10 MB/s.

The Fast ATA-2 or Enhanced IDE (EIDE) interface, using both traditional (but extended) addressing by head, cylinder and sector numbers, and addressing logical blocks (Logic Block Address LBA), supports disk capacity up to 2500 MB and transfer speeds up to 16 MB/s. Using EIDE, up to four drives can be connected to the motherboard, including CD-ROM and NKML. Older BIOS versions require a special driver to support EIDE.

Along with ATA and ATA-2, two versions of more complex Small Computer System Interface disk interfaces are also widely used: SCSI and SCSI-2. Their advantages: high data transfer speed (the Fast Wide SCSI-2 interface and the soon-to-be-expected SCSI-3 interface support speeds of up to 40 MB/s), a large number (up to 7 pcs.) and maximum capacity of connected drives. Their disadvantages: high cost (about 5-10 times more expensive than ATA), complexity of installation and configuration. SCSI-2 and SCSI-3 interfaces are designed for use in powerful server machines and workstations.

To increase the speed of processor data exchange with disks, HDDs should be cached. The disk cache has the same functionality as the main memory cache, i.e. serves as a high-speed memory buffer for short-term storage of information read or written to disk. Cache memory can be built into the drive, or it can be created programmatically (for example, by the Microsoft Smartdrive driver) in RAM. The speed of processor data exchange with disk cache memory can reach 100 MB/s.

A PC usually has one, or less often several, hard disk drives. However, in MS DOS (MicroSoft Disk Operation System - Microsoft's disk operating system), one physical disk can be divided into several "logical" disks by software; thereby simulating several NMDs on one drive.

3. RAID disk arrays

In database server machines and supercomputers, RAID (Redundant Array of Independent Disks) disk arrays are often used, in which several hard drives are combined into one large logical disk, based on the introduction of information redundancy. methods for ensuring the reliability of information, significantly increasing the reliability of the system (if distorted information is detected, it is automatically corrected, and the faulty drive is replaced with a working one in Plug and Play mode).

There are several levels of basic RAID array layout:

Level 1 includes two disks, the second of which is an exact copy of the first;

Level 2 uses multiple disks specifically to store checksums and provides the most functionally sophisticated and most efficient method of error correction;

Level 3 includes four disks: three are informational, and the fourth stores checksums that ensure error correction in the first three;

Levels 4 and 5 use disks, each of which stores its own checksums.

Second generation disk arrays - RAID6 and RAID7. The latter can combine up to 48 physical disks of any capacity, forming up to 120 logical disks; have an internal cache memory of up to 256 MB and connectors for connecting external SCSI interfaces. The internal X-bus has a throughput of 80 MB/s (for comparison: SCSI-3 transfer is up to 40 MB/s, and the read speed from a physical disk is up to 5 MB/s).

The mean time between failures in RAID disk arrays is hundreds of thousands of hours, and with the 2nd level of layout it is up to a million hours. In conventional NMD this value does not exceed a thousand hours. The information capacity of RAID disk arrays is from 3 to 700 GB (the maximum capacity of disk drives achieved in 1995 was 5.5 TB = 5500 GB).

HDDs with removable packages and disks (Bernoulli drives) are also used, using packages of disks with a diameter of 133 mm; they have a capacity of 20 to 230 MB and lower speed, but more expensive than hard drives. Their main advantage: the ability to accumulate and store packages outside of a PC.

The main directions for improving the characteristics of NMD:

use of highly efficient disk interfaces (E1DE, SCSI); the use of more advanced magnetic heads, which allows increasing the recording density and, consequently, the disk capacity and transfer (without increasing the disk rotation speed).

4. CDs .

General information about CDs

In 1982, Sony and Philips completed work on the CD audio format (Compact Disk), thereby ushering in the era of digital media on compact discs. The operating principle of these discs is optical. Reading and writing is carried out by a laser. In a CD, data is encoded and recorded as a sequence of reflective and non-reflective sections. The reflection is interpreted as one, the “valley” as zero.

I will give some technical parameters of CDs. The operating wavelength of the laser is 780 nm. CD diameter 120 mm. Disc thickness 1.2 mm. Disc capacity 700 MB (74 min audio). Weight 14-33 g. The chain of pits is arranged in a spiral, like in a gramophone record, but away from the center (in fact, a CD is a sequential access device with fast rewinding). The interval between turns is 1.6 µm, pit width is 0.5 µm, depth is 0.125 µm (1/4 wavelength of the laser beam in polycarbonate), minimum length is 0.83 µm (Fig. 1).

Rice. 1. CD surface.

There are modifications of 80 minutes (700 MB), 90 minutes (791 MB) and 99 minutes (870 MB). Nominal (1x) data transfer rate is 150 KB/sec (176400 bytes/sec audio or “raw” data, 4.3 Mbit/sec “physical” data). While all magnetic disks rotate at a constant number of revolutions per minute, that is, with a constant angular velocity (CAV, Constant Angular Velocity), a compact disk usually rotates at a variable angular velocity to provide a constant linear speed when reading (CLV, Constant Linear Velocity). Thus, reading the internal sides is carried out with an increased number of revolutions, and the external ones - with a reduced number of revolutions. This is what determines the rather low data access speed for CDs compared, for example, with hard drives.

Classification of CDs

There are many standards and formats for CDs, depending on the purpose and manufacturers. I will give as an example not all existing ones: Audio CD (CD-DA), CD-ROM (ISO 9660, mode 1 & mode 2), Mixed-mode CD, CD-ROM XA (CD-ROM eXtended Architecture, mode 2, form 1 & form 2), Video CD, CD-I (CD-Interactive), CD-I-Ready, CD-Bridge, Photo CD (single & multi-session), Karaoke CD, CD-G, CD-Extra, I -Trax, Enhanced CD (CD Plus), Multi-session CD, CD-Text, CD-WO (Write-Once). A full description of them would take too much space, and this is not the purpose of writing this work.

Depending on the number of possible recording operations, CDs are divided into: CD-ROM (read only memory), CD-R (recordable), also known as CD-WORM (write once read many), CD-RW (rewritable). Accordingly, the CD-ROM is manufactured at the factory, and further recording on it is impossible; CD-R is intended to be written once at home; CD-RW allows many write operations. CD-ROM discs are polycarbonate, coated on one side with a reflective layer (aluminum or - for critical applications - gold) and a protective varnish on the other. The reflectivity is changed by stamping recesses in the metal layer. At the factory they are simply stamped from the matrix.

CD format

The surface of the disk is divided into areas:

· PCA (Power Calibration Area). Used to adjust the laser power of the recording device. 100 elements.

· PMA (Program Memory Area). The coordinates of the beginning and end of each track are temporarily recorded here when the disc is removed from the recording device without closing the session. 100 elements.

· Lead-in Area - a 4 mm wide ring (diameter 46-50 mm) closer to the center of the disk (up to 4500 sectors, 1 minute, 9 MB). Consists of 1 track (Lead-in Track). Contains TOC (absolute temporary addresses of tracks and the beginning of the output area, accuracy - 1 second).

· Data area (program area, user data area).

· Lead-out area - ring 116-117 mm (6750 sectors, 1.5 minutes, 13.5 MB). Consists of 1 track (Lead-out Track).

Each byte of data (8 bits) is encoded into a 14-bit character on the medium (EFM encoding). Characters are separated by 3-bit spaces, chosen so that there are no more than 10 consecutive zeros on the medium.

From 24 bytes of data (192 bits) a frame (F1-frame) is formed, 588 bits of media, not counting the spaces:

· synchronization (24 bit media)

· subcode symbol (bits of subchannels P, Q, R, S, T, U, V, W)

· 12 data characters

· 4 character control code

· 12 data characters

· 4 character control code

Decoding may use different strategies for detecting and correcting group errors (probability of detection vs. reliability of correction).

A sequence of 98 frames forms a sector (2352 information bytes). The frames in the sector are shuffled to reduce the impact of media defects. Sector addressing originates from audio discs and is written in A-Time format - mm:ss:ff (minutes:seconds:beats, fractions per second from 0 to 74). The countdown starts from the beginning of the program area, i.e. the sector addresses of the input area are negative. The subchannel bits are assembled into 98-bit words for each subchannel (of which 2 bits are synchronization). Subchannels used:

· P - marking the end of the track (min 150 sectors) and the beginning of the next (min 150 sectors).

· Q - additional information about the contents of the track:

o number of channels

o data or sound

o is it possible to copy

o sign of frequency pre-emphasis: artificial increase in high frequencies by 20 dB

o subchannel usage mode

Q-Mode 1: The input area stores the TOC here, the program area stores track numbers, addresses, indexes and pauses

Q-Mode 2: disk catalog number (same as on the barcode) - 13 digits in BCD format (MCN, ENA/UPC EAN)

Q-Mode 3: ISRC (International Standard Recording Code) - country code, owner, year and serial number of the recording

A sequence of sectors of the same format is combined into a track (track) from 300 sectors (4 seconds, see subchannel P) to the entire disc. A disc can have up to 99 tracks (numbered 1 to 99). A track may contain service areas:

· pause - only subchannel information, no user data

· pre-gap - the beginning of the track, does not contain user data and consists of two intervals: the first, at least 1 second long (75 sectors), allows you to “build up” from the previous track, the second, at least 2 seconds long, sets the format of the track sectors

· post-gap - end of track, does not contain user data, at least 2 seconds long

The lead-in digital area must end with a post-gap. The first digital track must start from the second part of the pre-gap. The last digital track must end with a post-gap. The output digital area does not contain pre-gap.

Practical part

Option 14

Using PPP on a PC, it is necessary to determine the cost of maintaining one student in an extended day group in a city school per year based on available data.

Calculate:

· The amount of expenses for food for the student in the current and projected year;

· The amount of expenses for maintaining a student in the current and projected year;

· Absolute and relative changes in the calculated indicators of the projected year to the indicators of the current year in the form of a table.

Enter the current date value between the table and its title.

Using the table data, construct a histogram with a title, the name of the coordinate axes and a legend.

1. Selection of PPP.

In this task, it is most advisable to apply and use the MS Excel spreadsheet processor. Since it can most fully reflect the algorithm of work, design and graphical representation of data forms for our task.

2. Description of the algorithm for solving the problem.

TC is the total cost of maintaining one student, Z is wages, D is accruals on wages, C is the cost of soft equipment, N is the norm for food per day, K is the number of days the groups operate.

Amount of food expenses N*K

Amount of student maintenance expenses Z+(Z*D/100)+C

Absolute change in the calculated indicators of the projected year to the indicators of the current one: ABS project – ABS current

Relative change in the calculated indicators of the projected year to the current indicators: (ABS project – ABS current)*100/(N*K) current

Designing forms of output documents and graphical presentation of data on the selected task.

3 Structure of table templates

Table.1 “Costs per student”

Table 2 Costs of maintaining one student in an extended day group in a city school per year

4 Arrangement of tables on MS Excel worksheets.

Table 3 Costs of maintaining one student

Table 4. Final table of the costs of maintaining a student in an extended day group in a city school.

5 Table templates with source data

Table 6 Costs of maintaining one student

Table 6 Costs of maintaining one student in an extended day group in a city school per year.

Index	this year	project year	Absolute change in the calculated indicators of the projected year to the indicators of the current year (rub)	Relative change in the calculated indicators of the projected year to the indicators of the current year (%)
Amount of expenses for student meals, rub.
Amount of expenses for maintaining a student, rub.	C10+(C11*C10/100)+C12	D10+(D11*D10/100)+D12
Total (RUB):	SUM(C24:C25)	SUM(D24:D25)	SUM(E24:E25)	SUM(F24:F25)

6 User's Manual.

The sequence of user actions when solving a problem:

To launch MS Excel from the main Windows menu, press the button Start and choose MS Excel on the menu Programs.

We enter the initial data into the spreadsheet of the cash order form

1. After you have entered the initial data, select the required cells, select the cell format and mark the required data type (numeric, date, text, currency), in the monetary format select the number of decimal places

2. Select the entire table and copy it to a new sheet.

3. On a new sheet, select the entire table and select it in the toolbar Data →Filter→ Autofilter. Using an autofilter, we can filter data by recipients and payment types.

4. Using the amount field, we summarize the total and use it to display the total when filtering the data. Inserting a function →mathematical→SUBTOTAL Next, select the amount data area.

7 Chart technology

· Press the button Chart Wizard on the toolbar Standard.

· We construct the required diagram:

Step 1. Choose Type (Histogram) and View (Plain) diagrams, press the button Further.

Step 2. Click the bookmark Row, in the window Row delete if there are extra rows, Click add row, then select the desired range in our case (marginal costs and marginal revenue) in the window x-axis labels click the checkbox:

In the window Chart Data Source indicate the range

name of the product by highlighting the corresponding zone in

table, click the checkbox, click the button Further.

Step 3. Select the required headings and press the button

Step 4. We follow the instructions Chart Wizards and press

button Ready.

Place the cursor in an empty space in the diagram and click

click the mouse and hold the button and drag the diagram onto

required field Liszt.

Click on any point on the Chart Area frame and stretch the chart frame to the desired size.

Conclusion

In this coursework we examined the topic “External computer memory”. We also completed the practical part using the MS Excel spreadsheet processor. Since it can most fully reflect the algorithm of work, design and graphical representation of data forms for our task.

In the theoretical part, we looked at the types of external memory:

· Magnetic disks (MD)

· Hard disks

RAID disk arrays

· CDs

They also gave a definition of external computer memory. It usually means both storage media (that is, devices where it is directly stored) and devices for reading/writing information, which are most often called drives.

Bibliography

1. Gein A.G., Senokosov A.I., Sholokhovich V.F. Computer science: 7-9 grades. Textbook for general education textbook establishments - M.: Bustard, 2002.

2. Kaimin V.A., Shchegolev A.G., Erokhina E.A., Fedyushin D.P. Fundamentals of Informatics and Computer Science: Prob. textbook for 10-11 grades average. schools. - M.: Education, 2001.

3. Kushnirenko A.G., Lebedev G.V., Svoren R.A. Fundamentals of Informatics and Computer Science: Textbook. for average textbook establishments. - M.: Education, 2003.

4. Semakin I., Zalogova L., Rusakov S., Shestakova L. Informatics: textbook. at the basic rate. - M.: Laboratory of Basic Knowledge, 1999.

5. Ugrinovich N. Informatics and information technologies. Textbook for educational institutions. - M.: BINOM, 2003. - 464 p. (§ 2.14. Information storage, pp. 91-98).

External memory (ERAM) is designed for long-term storage of programs and data, and the integrity of its contents does not depend on whether the computer is turned on or off. This type of memory has a large capacity and low speed. Unlike RAM, external memory does not have a direct connection with the processor. Information from the OSD to the processor and vice versa circulates approximately along the following chain:

The computer's external memory includes:

hard disk drives;

floppy disk drives;

CD drives;

magnetic tape drives (streamers);

Magnetic-optical disk drives;

HDD

Hard disk (hard magnetic disk drives, HDD) is a type of permanent memory. Unlike RAM, data stored on a hard drive is not lost when the computer is turned off, making the hard drive ideal for long-term storage of programs and data files, as well as the most important operating system programs. This ability (keeping information intact and safe after shutdown) allows you to remove a hard drive from one computer and insert it into another.

When you turn on your computer, the BIOS performs a POST (Power On Self Test) and checks to see if there is a floppy disk in the drive. If there isn't one, it goes to the hard drive and copies a short program called "boot memory" from the hard drive to RAM. It then transfers control of the computer to a boot program, which oversees the loading of the operating system. Once the system is booted, the boot program is erased from memory, transferring control of the computer to the fully loaded operating system.

Hard drives are very reliable for storing large amounts of information and data. Inside a sealed hard drive are one or more inflexible disks coated with metal particles. Each disk has a head (a small electromagnet) built into an articulated arm that moves over the disk as it rotates. The head magnetizes the metal particles, causing them to line up to represent the ones and zeros of binary numbers. The motors that move the disc and lever are usually subject to wear and tear. Only the head can avoid wear, since it never comes into contact with the surface of the disc.

Another function of a hard drive is RAM simulation. By using sections of the hard drive as virtual memory, Windows can run more programs. The disadvantage of virtual memory is that it is slow compared to regular memory. If you set more, your computer will slow down.

The hard drive, or hard drive, is the most important component of a computer. It stores the operating system, programs and data. Without the Windows operating system, you cannot start your computer, and without programs, you cannot do anything once it has already booted. Without a data bank, you will have to enter information manually each time.

The hard drive is a mechanical device in the computer and can cause more problems than electronic devices. It's actually very reliable. The discs are collected in clean rooms in which the air is constantly filtered and dust particles are removed. Hard drives are assembled from magnetically sensitive material. Before the discs are taken out of the room, they are packaged and sealed. If you open your hard drive out of curiosity, you can say goodbye to it. To prevent this from happening, never do this - you cannot open them.

New hard drives must be formatted before use. This process consists of laying magnetic concentric paths and breaking them into small sectors, like pieces in a cake. Be careful: if data was written to the hard drive, formatting it will completely destroy it.

Due to the much larger number of tracks on each side of the disks and the large number of disks, the information capacity of a hard disk can be hundreds of thousands of times greater than the information capacity of a floppy disk and reach 150-200 GB. The speed of writing and reading information from hard drives is quite high (can reach 133 MB/s) due to the fast rotation of the disks (up to 7200 rpm).

Hard drives use rather fragile and miniature elements (media platters, magnetic heads, etc.), therefore, in order to preserve information and performance, hard drives must be protected from shocks and sudden changes in spatial orientation during operation.

Floppy disk drives

Disk drives (floppy disk drives (FDD)) come in two main types - for large floppy disks (5.25 inches in size, sometimes written 5.25"), and for small ones (3.5 inches, 3. 5"). A five-inch floppy disk can hold, depending on its type, from 360 information (360 thousand characters) to 1.2 MB. Three-inch cards, although smaller, hold more information (720 KB - 1.44 MB). In addition, the three-inchers are enclosed in a plastic case, and therefore are more difficult to break or dent. The standard disk drive for modern computers is the small (3.5-inch) floppy disk drive. Hence its name in a computer system - 3.5 A drive.

The 5-inch drive is located on the front of the computer system unit and looks like a slot with a latch lever into which the floppy disk is inserted and latched. The 3-inch drive has a smaller slot (by 2 inches), and instead of a latch it has a button.

A floppy drive is more similar to a magnetic tape drive than a hard drive. Its head physically contacts the floppy disk and thus magnetizes the surface, protected from dust by a moving flap that automatically retracts when the disk is inserted into the drive.

Floppy drives supply data to the system through a cable connected to a connector on the motherboard. It is different from the IDE controller used for hard drives and the data transfer speed is much slower.

Floppy disk drives are becoming little used, but still necessary. They are used only for transferring small amounts of data from one computer to another, as well as for emergency computer startup. CD-ROM drives are the primary method for distributing new software, but they are not required by the computer to perform data processing functions.

Flexible magnetic disks. Two main types

A floppy disk or floppy disk is a medium of small amounts of information, which is a flexible plastic disk in a protective (plastic) shell. Used to transfer data from one computer to another and to distribute software.

In the center of the floppy disk there is a device for gripping and rotating the disk inside the plastic case. The floppy disk is inserted into the disk drive, which rotates the disk at a constant angular speed.

In this case, the magnetic head of the disk drive is installed on a certain concentric track of the disk, onto which information is written or from which information is read. The information capacity of a modern floppy disk is small and amounts to only 1.44 MB. The speed of writing and reading information is also low (only about 50 KB/s) due to the slow rotation of the disk (360 rpm).

In order to preserve information, flexible magnetic disks must be protected from exposure to strong magnetic fields (for example, do not place a mobile phone next to a floppy disk) and heat, since such physical effects can lead to demagnetization of the media and loss of information.

Currently, the most widespread are floppy disks with the following characteristics: diameter 3.5 inches (89 mm), capacity 1.44 MB, number of tracks 80, number of sectors on tracks 18 (Floppy disks with a diameter of 5.25" are now used very rarely, so their capacity does not exceed 1.2 MB, and besides, they are made of less durable material). spins up to a rotation speed of 360 per minute. The diskette itself rotates in the drive, the magnetic heads remain stationary only when it is accessed.

Recently, three-inch floppy disks have appeared that can store up to 3 GB of information. They are manufactured using the new Nano2 technology and require special hardware for reading and writing, which is not yet included in the standard package when purchasing a PC.

Floppy disk device

Floppy disks vary in size and capacity. By size, the division is made into floppy disks with a diameter of 5.25" (" - inch sign) and floppy disks with a diameter of 3.5". In terms of capacity - double density floppy disks (in English double density, abbreviation - DD) and high density (abbreviation - HD).

A 5.25" floppy disk consists of a protective plastic sleeve containing a magnetically coated plastic disk. This disk is thin and bends easily - that's why floppy disks are called floppy disks. Of course, you cannot bend the floppy disk, and this is prevented by the protective sleeve. The floppy disk has two holes - a large one in the center and a small one next to it. The large hole is designed to allow the magnetic disk to rotate inside the envelope.

This is done by a motor inside the drive. The inside of the protective envelope is covered with lint, which collects dust from the magnetic disk as it rotates. The small hole is used to count the revolutions of the disk inside the drive. The envelope has a longitudinal slot on both sides through which a disk with a magnetic coating is visible. Through this slot, a magnetic head inside the drive touches the disk and writes or reads data from it. Data is written to both sides of the disk. Never touch the surface of the magnetic disk with your fingers! By doing this, you can ruin it by scratching or greasy. If you turn the floppy disk with the slot facing you, with the label facing up, you will see a small rectangular cutout on the top right side of the envelope. If you cover it with pieces of sticky paper (usually sold with floppy disks), the disk will be write-protected. Typically, this cutout should be free; it should only be sealed on floppy disks with important data.

The structure of a 3.5" floppy disk is slightly different. Its protective sleeve is made of hard plastic, so such a floppy disk is more difficult to bend or break. The magnetic disk is not visible, since there are no open holes. There is a slot for access of the magnetic head to the surface of the disk, but it is covered with a latch. The latch is held closed by a spring. You do not need to open it with your hands to avoid damaging the magnetic disk. Inside the drive, the latch opens automatically. For write protection, the floppy disk has a small latch on the top left of the floppy disk if you hold the floppy disk with the large latch facing you. , with the label facing down. The write latch down position is normal; in this state, the floppy disk is not write-protected. To prevent data from being written to the floppy disk, slide the latch upward to reveal a small square hole in the diskette.

Floppy disk recording method

The method of recording binary information on a magnetic medium is called magnetic coding. It lies in the fact that magnetic domains in the medium are aligned along paths in the direction of the applied magnetic field with their north and south poles. Typically, a one-to-one correspondence is established between binary information and the orientation of magnetic domains.

Information is recorded along concentric tracks (tracks), which are divided into sectors. The number of tracks and sectors depends on the type and format of the floppy disk. A sector stores the minimum amount of information that can be written to or read from disk. The sector capacity is constant and amounts to 512 bytes.

A CD-ROM writer can record any type of information - music, images or text. There are recordable discs on which you can write information only once (CD-R). But there are also rewritable discs (CD-RW), they are more expensive, but they allow you to erase information and add new information. However, if you burn music to a rewritable CD, you can only listen to it on your PC, but the rewritable disc can only be played on any CD player.

Optical principle of recording and reading information.

Laser CD-ROM and DVD-ROM drives use the optical principle of recording and reading information.

In the process of recording information on laser discs, various technologies are used to create surface areas with different reflectance coefficients: from simple stamping to changing the reflectivity of areas of the disc surface using a powerful laser. Information on a laser disk is recorded on one spiral-shaped track (like on a gramophone record), containing alternating sections with different reflectivity.

In the process of reading information from laser disks, a laser beam installed in the disk drive falls on the surface of the rotating disk and is reflected. Since the surface of the laser disk has areas with different reflection coefficients, the reflected beam also changes its intensity (logical 0 or 1). Then the reflected light pulses are converted using photocells into electrical pulses and transmitted via the highway to the RAM.

Subject to proper storage (in cases in a vertical position) and operation (without causing scratches or contamination), optical media can retain information for decades.

Laser drives and disks

Laser drives (CD-ROM and DVD-ROM) use the optical principle of reading information.

Laser CD-ROM (CD - Compact Disk) and DVD-ROM (DVD - Digital Video Disk) disks store information that was recorded on them during the manufacturing process. It is impossible to write new information to them, which is reflected in the second part of their names: ROM (Real Only Memory - read only). Such discs are produced by stamping and have a silver color.

The information capacity of a CD-ROM drive can reach 650-700 MB, and the speed of reading information in a CD-ROM drive depends on the rotation speed of the disc. The first CD-ROM drives were single-speed and provided information reading speeds of 150 KB/s. Currently, 52-speed CD-ROM drives are widely used, which provide 52 times faster information reading speed (up to 7.8 MB/s).

DVDs have a much larger information capacity (up to 17 GB) compared to CDs. First, lasers with shorter wavelengths are used, which allows the optical tracks to be placed more densely. Secondly, information on DVDs can be recorded on two sides, with two layers on one side.

The first generation of DVD-ROM drives provided information reading speeds of approximately 1.3 MB/s. Currently, 16-speed DVD-ROM drives achieve read speeds of up to 21 MB/s.

There are CD-R and DVD-R discs (R - recordable) that are golden in color. Information on such disks can be written, but only once. On CD-RW and DVD-RW (RW - ReWritable) discs, which have a "platinum" tint, information can be recorded many times.

For recording and rewriting onto discs, special CD-RW and DVD-RW drives are used, which have a fairly powerful laser that allows you to change the reflectivity of surface areas during the recording process. These drives allow you to write and read information from disks at different speeds. For example, marking a CD-RW drive “40x12x48” means that CD-R discs are written at 40x speed, CD-RW discs are written at 12x speed, and CD-RW discs are read at 48x speed.

Magnetic tape drives (streamers) and removable disk drives

Streamer (English tape streamer) - a device for backing up large amounts of information. The media used here are magnetic tape cassettes with a capacity of 1 - 2 GB or more.

Streamers allow you to record a huge amount of information onto a small magnetic tape cassette. The hardware compression tools built into the tape drive allow you to automatically compress information before recording it and restore it after reading it, which increases the amount of stored information.

The disadvantage of streamers is their relatively low speed of recording, searching and reading information. At the moment, streamers are outdated and therefore they are used very rarely in practice.

Recently, storage devices on removable disks have become increasingly used, which allow not only increasing the amount of stored information, but also transferring information between computers. The volume of removable disks ranges from hundreds of MB to several gigabytes.

External memory
External memory- this is memory implemented in the form of external (relative to the motherboard) storage devices (VSD) with different principles for storing information.
VZU are intended for long-term storage of information of any type and are characterized by a large amount of memory and low performance compared to RAM.
External computer memory is usually understood as a device for reading / writing information - drives, and devices where information is directly stored - carriers information.
As a rule, each storage medium has its own storage device. A device such as a hard drive combines both a storage medium and a storage device.
The storage media in the external memory of modern computers are magnetic and optical disks, magnetic tapes and some others.
The main types of external (long-term) memory devices based on recording method are:
In personal computers, external memory devices include:
Floppy disk drives designed for reading/writing information on floppy disks (floppy disks);
Hard magnetic disk drives, or hard drives;
disk drives for working with laser (optical) disks;
streamers designed for reading/writing information on magnetic tapes;
Magneto-optical drives for working with magneto-optical disks;
Non-volatile memory devices (flash memory).

Based on the type of access to information, external memory devices are divided into two classes:
Devices direct (random) access.
In direct (random) access devices, the time of accessing information does not depend on its location on the media. For example, to listen to a song recorded on a gramophone record, it is enough to install the pickup of the player in the place on the record where the song was recorded.
Devices sequential access.
In serial access devices such a dependence exists. For example, the access time to a song on an audio cassette depends on the location of the recording. To listen to it, you must first rewind the cassette to the place where the song was recorded.

Capacity (volume)- the maximum amount of information (data volume) that can be written to the medium.
Performance determined by the access time to the required information, the time it takes to read/write it, and the data transfer rate.

The capacity of external memory is hundreds and thousands of times greater than the capacity of RAM or even unlimited when it comes to drives with removable media.
But accessing external memory requires much more time, since the speed of external memory is significantly lower than that of RAM.

The main function of external memory is the ability to store information for a long time. In addition, external memory has a large capacity and is cheaper than RAM. And yet, external memory media ensure the transfer of information from one computer to another, which is important in a situation where there are no computer networks.

Thus, external (long-term) memory- this is a place for long-term storage of data (programs, calculation results, texts, etc.) not currently used in the computer’s RAM. External memory, unlike RAM, is non-volatile and has no direct connection with the processor.

To work with external memory, you must have a drive (a device that provides recording and (or) reading of information) and a storage device - a carrier.

Main types of storage devices:

floppy magnetic disk drives (FMD);

hard magnetic disk drives (HDD);

CD-ROM, CD-RW, DVD drives. The main types of media correspond to them:

flexible magnetic disks (Floppy Disk);

hard magnetic disks (Hard Disk);

CD-ROM, CD-R, CD-RW, DVD discs. Main characteristics of drives and media:

information capacity;

speed of information exchange;

reliability of information storage;

The basis for recording, storing and reading information from external memory is based on two principles - magnetic and optical. Thanks to these principles, information is retained even after the computer is turned off.

floppy disk

A floppy disk drive or floppy disk is a storage medium for a small amount of information, which is a flexible disk in a protective shell. Used to transfer data from one computer to another and to distribute software.

The disc is located inside a plastic sleeve, which protects it from mechanical damage. They may be damaged if:

touch the recording surface;

write on the floppy disk label with a pencil or ballpoint pen;

bend a floppy disk;

overheat the floppy disk (leave it in the sun or near a radiator);

expose the floppy disk to magnetic fields

The disk inside the drive rotates at a constant angular speed, which is quite low (several kilobytes per second, average access time - 250 ms). Information is written to both sides of the disk. Currently, the most common floppy disks are 3.5 inches in size (1 inch = 2.54 cm) and have a capacity of 1.44 MB. The disc can be write protected. A safety latch is used for this purpose. Floppy disks require careful handling.

Hard magnetic disk

The hard drive is informational

computer warehouse and is capable of storing

huge amounts of information.

Hard magnetic storage

disks(English)HDD - HardDiskDriver)

or Vinchester- this is the most widespread Fig.2. Hard magnetic disk

A high-capacity storage device in which the information carriers are aluminum plates, both surfaces of which are coated with a layer of magnetic material. Used for permanent storage of programs and data. The hard drives are placed on one axis and, together with the read/write heads and the heads that carry them, are placed in a hermetically sealed metal case. This design made it possible to significantly increase the disk rotation speed and recording density. Information is written to both surfaces of the disks

Unlike a floppy disk, a hard disk spins continuously. The platters in a hard drive rotate at a certain speed (also called spindle speed), which can be 3,600, 4,200, 5,400, 7,200, 10,000 or 15,000 rpm

Therefore, its rotation speed can be from 3600 to 10,000 rpm, data search time can be from 2 to 6 ms, and data transfer speed can be up to 300 MB/sec. The capacity of hard drives in computers is measured in tens of gigabytes. The most common drives with a diameter of 0.8, 1, 1.8, 2.2 inches.

In order to preserve information and performance, the hard drive must be protected from shocks and sudden changes in spatial orientation during operation.

Laser disc

CD- ROM(English)CompactDiskRealOnlyMemory-I constantly remembergeneral device based on a CD)

The CD has a diameter of 120 mm (about 4.75 inches) and is made of polymer and coated with a metal film. Information is read from this metal film, which is coated with a polymer that protects the data from damage. CD-ROM is a one-sided storage medium.

The principle of digital recording of information on a laser disk differs from the principle of magnetic recording. The encoded information is applied to the disk with a laser beam, which creates microscopic depressions on the surface, separated by flat areas. Digital information is represented by alternating depressions (coding zero) and light-reflecting islands (coding one). The information stored on the disk cannot be changed.

Data access on a CD-ROM is faster than data on floppy disks, but slower than on hard drives (150 to 400 ms at speeds up to 4500 rpm). The data transfer speed is at least 150 KB and reaches 1.2 MB/s. CD-ROM capacity reaches 780 MB, due to which multimedia programs are usually released on them.

CD-ROMs are simple and easy to use, have a low unit cost of data storage, practically do not wear out, cannot be affected by viruses, and it is impossible to accidentally erase information from them.

CD-R (Compact Disk Recorder)

CD-R is a recordable disc with an average capacity of 700 MB (80 minutes). On CD-R discs, the reflective layer is made of gold film. Between this layer and the base there is a recording layer of organic material that darkens when heated. During the recording process, the laser beam heats selected points on the layer, which darken and stop transmitting light to the reflective layer, forming areas similar to depressions. CD-R drives, thanks to their significant reduction in price, are becoming increasingly widespread.

CD-RW (Compact Disk Rewritable)

More popular are CD-RW drives, which allow you to write and rewrite information. The CD-RW drive allows you to write and read CD-R and CD-RW discs, read CD-ROM discs, i.e. is in a certain sense universal.

The abbreviation DVD stands for DigitalVersatileDisk, i.e. uniuniversal digital disk. Having the same dimensions as a regular CD and a very similar operating principle, it holds an extremely large amount of information - from 4.7 to 17 GB. Perhaps it is precisely because of its large capacity that it is called universal. True, today the DVD disc is actually used in only two areas: for storing video films (DVD-Video or simply DVD) and ultra-large databases (DVD-ROM, DVD-R).

The discrepancy in capacities arises as follows: unlike CD-ROMs, DVDs are recorded on both sides. Moreover, one or two layers of information can be applied on each side. Thus, single-sided single-layer discs have a capacity of 4.7 GB (they are often called DVD-5, i.e. discs with a capacity of about 5 GB), double-sided single-layer - 9.4 GB (DVD-10), single-sided double-layer - 8.5 GB (DVD-9), and double-sided double-layer - 17 GB (DVD-18).

In order to preserve information, laser discs must be protected from mechanical damage (scratches), as well as from contamination.

Flash-memory

Flash-memory is a volatile type of memory that allows you to record and store data in microcircuits. Flash memory cards do not have moving parts, which ensures high data safety when used in mobile devices

(laptop computers, digital cameras, etc.)

Flash memory is a chip housed in a miniature flat package. To read or write information, the memory card is inserted into special drives built into mobile devices or connected to a computer via a USB port. The information capacity of memory cards is different, it can reach from 512 MB to 4 GB, 8 GB, 16 GB, 32 GB, 48 GB. Transcend has updated the popular JetFlash V20 series of USB flash drives by releasing a new model with a capacity of 64 GB.

The disadvantages of flash memory include the fact that there is no single standard and different manufacturers produce memory cards that are incompatible with each other in size and electrical parameters.

Smart electronic machines have long been firmly established in human everyday life. But despite this, their device still raises basic questions among many users. For example, not everyone knows what types of memory there are. But here everything is not so complicated, although not entirely simple. There are two main types - internal memory and external, which, in turn, have their own gradation.

Types of internal computer memory

Internal memory is so called because it is built into the main units of the computer and is an integral element of the system, ensuring its performance. It is impossible to remove or extract it without negative consequences. The following types are distinguished:

operational – is a set of programs and algorithms necessary for the operation of the microprocessor;
cache memory – this is a kind of buffer between the RAM and the processor, which ensures optimal execution speed of system programs;
constant – laid down when the computer is manufactured at the factory, it includes tools for monitoring the state of the PC at each boot; programs responsible for starting the system and performing basic actions; system setup programs;
semi-permanent – contains data about the settings of a specific PC;
video memory – it stores video fragments that should be displayed on the screen; it is part of the video controller.

Types of computer RAM

The performance and “intellectual level” of a computer are largely determined by its RAM. It stores data used during active operation of the electronic machine. It can also be of different types, but the most commonly used blocks are DDR, DDR2, DDR3. They differ in the number of contacts and speed characteristics.

Types of external computer memory

External computer memory is represented by various types of removable storage media. Today, the main ones are hard drives, USB drives, or flash drives and memory cards. Laserdiscs and floppy disks are considered obsolete. But, although it is removable, it is still used as a storage unit for permanent memory and the computer will not work without it. However, it can be freely removed and moved to another system unit, which is why it is classified as an external memory device.