The beginning of a new era. How DDR4 RAM works. Which RAM to prefer: DDR3 or DDR4

Computer technology is rapidly evolving, being replaced by new parameters and specifications, but RAM has a time advantage. DDR SDRAM was launched in 2000 and three years passed before the arrival of DDR2 SDRAM in 2003. DDR2 lasted four years and was replaced by DDR3 SDRAM in 2007. Since then, it has been unchanged for seven years, but the launch of DDR4 has taken place.

What's new in DDR4?

Externally, DDR4 is the same width as DDR3, but slightly taller by about 9mm. The difference between DDR3 and DDR4 is that DDR4 uses 288 pins compared to 240 on DDR3 and the key is located in a different location.

Lots of cosmetic changes, but four major improvements to DDR4 SDRAM:

Lower operating voltage
Increased energy savings
Frequency increase
Compaction of microcircuits.

DDR3 runs at 1.5V with modules running at 1.35V. DDR4 runs natively at 1.2V with modules running at 1.05V. Additionally, DDR4 supports a number of power saving enhancements by activating when the system is in standby mode.
The lower operating voltage allows DDR4 to consume less power (and therefore lower operating temperature) than DDR3.

DDR4 has an operating frequency of 2133MHz (this is the limit for DDR3), ultimately ending up at around 3200MHz. DDR4 chips can also be manufactured in densities of up to 16 GB (or 2 GB) per slab, which is twice the density of DDR3. This means that we will see consumer-grade hardware with a capacity of 16 GB, and 64 GB on the server-grade memory stick.

Cons of DDR4

Like most new technologies, DDR4 is not perfect. Prices will be 20-50% higher than the same DDR3 strips. As demand increases, the cost will come down, but for now DDR4 will simply be more expensive.
The second problem is that despite DDR4 clocking higher than DDR3, the timing is worse.

DDR3-2133MHz sticks usually have CL10-CL11, current DDR4-2133Mhz sticks will be CL15. This is not a surprise, the situation is repeated when DDR3 was introduced, but this does not mean that the fourth generation is inferior to its predecessor, just at first.
When comparing the Core i7 5960X and 4960X, Geekbench reports only slightly different scores with DDR4-2133MHz compared to DDR3-1600MHz (5691 vs 5382). Higher frequencies will be achieved in the near future, it remains to shorten the timing and we will see the power of DDR4.

Conclusion

RAM is a very important aspect of modern PCs. Fast memory is not bad, but performance capabilities are not the main advantage of DDR4 over DDR3.
DDR4 requires a completely different chipset and processor than DDR3, so DDR4 cannot be called a benchmark. A more detailed comparison of DDR4 / x99 / Haswell-E -VS- DDR3 Core i7 5960X in the article

Two things are most important: lower operating voltage and high memory density. With lower temperature conditions, components are much more reliable in relation to their counterparts.

Author's opinion

If I pick one aspect of DDR4 as the most important, memory density is my pick. This is a huge plus, which makes DDR4 more desirable in comparison to DDR3.

As programs and data types become larger and more complex, larger capacity RAM will become more and more important. Already about 33% based on X79 sold to Puget Systems, since January 2014 the amount of memory that can be installed in the system with 8x 8 GB sticks or 64 GB of RAM in total has already been exceeded. This is a huge part of Puget Systems' sales, as DDR4 has great potential and we would like to see it in high-performance workstations.

With the advent of the latest generation of processors from Intel - Skylake, laptop manufacturers have begun updating their range, releasing models that rely on this platform. The Chinese company Lenovo, for example, has released new ThinkPad E560 laptops, which, however, differ in one unusual solution. Despite the fact that they are equipped with the latest, sixth generation Intel processors, E560 laptops have older DDR3 memory, rather than DDR4, which we are used to seeing in most Skylake-based computers. The fact is that the mass introduction of the new DDR4 standard began with the announcement of this generation of processors, which can most effectively take advantage of the modern type of RAM. But what are they? How exactly is DDR4 superior to DDR3 and is the difference really that serious? We will try to answer these questions below.

A little background

Those who closely follow the technology industry know that, unlike microprocessors, computer memory is developing at a much more modest pace. For this reason, good old DDR3 memory was “stuck” on the market for eight years - an entire era for the world of high technology.

However, with the advent of new Skylake chips from Intel for DDR3, the time has come to retire, giving way to more promising DDR4 memory. This class of memory offers two main advantages: a significantly wider range of supported frequencies and reduced power consumption. In the case of DDR3, users have a choice between four fixed clock frequencies: 1333 MHz, 1600 MHz, 1866 MHz and 2133 MHz. Yes, there are still older versions with frequencies of 800 MHz and 1066 MHz, but the only place where you can find them is on fairly old computer systems.

The DDR4 standard in practice does not have an operating frequency ceiling - at least so far no manufacturer has managed to reach it. As soon as someone releases memory with a record clock speed, almost immediately another competitor offers an even faster solution. Sometimes it even comes to awkward cases - for example, G.Skill recently demonstrated a configuration containing four 32 GB DDR4 modules, each with a mind-blowing operating frequency of 3000 MHz, although earlier the same manufacturer released an 8 GB DDR4 memory module overclocked to 4266 MHz .

Another important advantage of DDR4 memory is its increased energy efficiency. For example, DDR3 memory as a standard requires a voltage in the range of 1.5 to 1.975 volts. The energy efficient version (DDR3L) requires up to 1.35 volts. At the same time, DDR4 will need 1.2 volts, but there is also a more economical option that needs only 1.05 volts.

In other words, DDR4 provides higher data transfer rates at lower power consumption levels, which of course makes it an ideal choice for all types of mobile devices. Increased efficiency also ensures greater stability of the computer system used for overclocking.

Finally, DDR4 raises the bar in another respect - the maximum amount of memory that can be installed on a single motherboard. For DDR3 the maximum ceiling is (theoretically) 128 GB, while for DDR4 it is four times higher - 512 GB.

Of course, at the moment there is not a single computer (with the exception of highly loaded server systems) that may require such a monstrous amount of memory, but in the coming years with the massive spread of technologies such as virtual and augmented reality or self-learning software modules such as Siri and Cortana, this may become the norm. Don’t forget that just ten years ago, RAM volumes like 16-32 GB also seemed unthinkable to us.

From theory to practice

All these advantages are simply a result of comparing the technical characteristics of both types of RAM. What does practice show? Currently, DDR4 is officially supported by a fairly narrow range of processors, namely the Haswell-E family from Intel and the latest generation of Skylake chips from the same manufacturer.

Despite numerous improvements for CPU-dependent applications and tasks, hands-on testing shows that most modern software is not ready to take full advantage of DDR4. For example, tests conducted by the Anandtech website show that when using the same processor (Skylake i7-6700K), the difference in the number of frames per second in almost all tested games is minimal and does not exceed 2-3 fps. The exception is the test with Grand Theft Auto V and using the graphics core built into the i7-6700K. In this comparison, the difference between DDR3 and DDR4 was 8 frames per second in favor of the new memory.

In performance applications such as archiving large volumes of data, DDR4 again shows superiority, but at the moment it is not as convincing.

Like any new technology, DDR4 takes time to establish itself in the market. Accordingly, during this time the software will have to “learn” to use the innovations offered by the new memory. For now, however, the big hope for the future of DDR4 lies not so much in desktop PCs, but in next-generation laptops, tablets and smartphones, where increased bandwidth with lower power consumption will be more welcome than ever.

Have a great day!

Here come the Intel Haswell-E processors. The site has already tested the top 8-core Core i7-5960X, as well as the ASUS X99-DELUXE motherboard. And, perhaps, the main feature of the new platform is support for the DDR4 RAM standard.

The beginning of a new era, the DDR4 era

About the SDRAM standard and memory modules

The first SDRAM modules appeared back in 1993. They were released by Samsung. And by 2000, SDRAM memory, due to the production capacity of the Korean giant, had completely ousted the DRAM standard from the market.

The abbreviation SDRAM stands for Synchronous Dynamic Random Access Memory. This can be literally translated as “synchronous dynamic random access memory”. Let us explain the meaning of each characteristic. Memory is dynamic because, due to the small capacitor capacity, it constantly requires updating. By the way, in addition to dynamic memory, there is also static memory, which does not require constant data updating (SRAM). SRAM, for example, is the basis of cache memory. In addition to being dynamic, the memory is also synchronous, unlike asynchronous DRAM. Synchronicity means that the memory performs each operation for a known amount of time (or clock cycles). For example, when requesting any data, the memory controller knows exactly how long it will take for it to get to it. The synchronicity property allows you to control the flow of data and queue it. Well, a few words about “random access memory” (RAM). This means that you can simultaneously access any cell at its address for reading or writing, and always at the same time, regardless of location.

SDRAM memory module

If we talk directly about the design of memory, then its cells are capacitors. If there is a charge in the capacitor, then the processor regards it as a logical unit. If there is no charge - as a logical zero. Such memory cells have a flat structure, and the address of each of them is defined as the row and column number of the table.

Each chip contains several independent memory arrays, which are tables. They are called banks. You can work with only one cell in a bank per unit of time, but it is possible to work with several banks at once. The information being recorded does not have to be stored in a single array. Often it is split into several parts and written to different banks, and the processor continues to consider this data as a single whole. This recording method is called interleaving. In theory, the more such banks in memory, the better. In practice, modules with a density of up to 64 Mbit have two banks. With a density of 64 Mbit to 1 Gbit - four, and with a density of 1 Gbit and higher - already eight.

What is a memory bank

And a few words about the structure of the memory module. The memory module itself is a printed circuit board with chips soldered on it. As a rule, you can find devices on sale made in the DIMM (Dual In-line Memory Module) or SO-DIMM (Small Outline Dual In-line Memory Module) form factors. The first is intended for use in full-fledged desktop computers, and the second is for installation in laptops. Despite the same form factor, memory modules of different generations differ in the number of contacts. For example, an SDRAM solution has 144 pins for connecting to the motherboard, DDR - 184, DDR2 - 214 pins, DDR3 - 240, and DDR4 - already 288 pieces. Of course, in this case we are talking about DIMM modules. Devices made in the SO-DIMM form factor naturally have a smaller number of contacts due to their smaller size. For example, a DDR4 SO-DIMM memory module is connected to the motherboard using 256 pins.

The DDR module (bottom) has more pins than SDRAM (top)

It is also quite obvious that the volume of each memory module is calculated as the sum of the capacities of each soldered chip. Memory chips, of course, can differ in their density (or, more simply, in volume). For example, last spring Samsung launched mass production of chips with a density of 4 Gbit. Moreover, in the foreseeable future it is planned to release memory with a density of 8 Gbit. Memory modules also have their own bus. The minimum bus width is 64 bits. This means that 8 bytes of information are transmitted per clock cycle. It should be noted that there are also 72-bit memory modules in which the “extra” 8 bits are reserved for ECC (Error Checking & Correction) error correction technology. By the way, the bus width of a memory module is also the sum of the bus widths of each individual memory chip. That is, if the memory module bus is 64-bit and there are eight chips soldered on the strip, then the memory bus width of each chip is 64/8 = 8 bits.

To calculate the theoretical bandwidth of a memory module, you can use the following formula: A*64/8=PS, where “A” is the data transfer rate, and “PS” is the required bandwidth. As an example, we can take a DDR3 memory module with a frequency of 2400 MHz. In this case, the throughput will be 2400*64/8=19200 MB/s. This is the number referred to in the marking of the PC3-19200 module.

How does information directly read from memory occur? First, the address signal is sent to the corresponding row (Row), and only then the information is read from the desired column (Column). The information is read into the so-called Sense Amplifiers - a mechanism for recharging capacitors. In most cases, the memory controller reads an entire packet of data (Burst) from each bit of the bus at once. Accordingly, when recording, every 64 bits (8 bytes) are divided into several parts. By the way, there is such a thing as data packet length (Burst Length). If this length is 8, then 8*64=512 bits are transmitted at once.

Memory modules and chips also have such a characteristic as geometry, or organization (Memory Organization). The module geometry shows its width and depth. For example, a chip with a density of 512 Mbit and a bit depth (width) of 4 has a chip depth of 512/4 = 128M. In turn, 128M=32M*4 banks. 32M is a matrix containing 16000 rows and 2000 columns. It can store 32 Mbit of data. As for the memory module itself, its width is almost always 64 bits. The depth is easily calculated using the following formula: the volume of the module is multiplied by 8 to convert from bytes to bits, and then divided by the bit depth.

You can easily find the timing values on the markings

It is necessary to say a few words about such characteristics of memory modules as timings. At the very beginning of the article, we said that the SDRAM standard provides for such a point that the memory controller always knows how long a particular operation takes to complete. Timings precisely indicate the time required to execute a specific command. This time is measured in memory bus clocks. The shorter this time, the better. The most important delays are:

TRCD (RAS to CAS Delay) - the time required to activate the bank line. Minimum time between activation command and read/write command;
CL (CAS Latency) - time between issuing a read command and the start of data transfer;
TRAS (Active to Precharge) - line activity time. The minimum time between activating a line and the command to close the line;
TRP (Row Precharge) - time required to close a row;
TRC (Row Cycle time, Activate to Activate/Refresh time) - time between activation of rows of the same bank;
TRPD (Active bank A to Active bank B) - time between activation commands for different banks;
TWR (Write Recovery time) - time between the end of writing and the command to close the bank line;
TWTR (Internal Write to Read Command Delay) - time between the end of the write and the read command.

Of course, these are not all the delays that exist in memory modules. You can list a dozen more different timings, but only the above parameters significantly affect memory performance. By the way, only four delays are indicated in the labeling of memory modules. For example, with parameters 11-13-13-31, the CL timing is 11, TRCD and TRP are 13, and TRAS is 31 clock cycles.

Over time, the potential of SDRAM reached its ceiling, and manufacturers were faced with the problem of increasing the speed of RAM. This is how the DDR.1 standard was born

The Coming of DDR

The development of the DDR (Double Data Rate) standard began back in 1996 and ended with the official presentation in June 2000. With the advent of DDR, SDRAM memory became a thing of the past and was simply called SDR. How does the DDR standard differ from SDR?

After all SDR resources were exhausted, memory manufacturers had several options to solve the problem of improving performance. It would be possible to simply increase the number of memory chips, thereby increasing the capacity of the entire module. However, this would have a negative impact on the cost of such solutions - this idea was very expensive. Therefore, the JEDEC manufacturers association took a different route. It was decided to double the bus inside the chip, and also transmit data at twice the frequency. In addition, DDR provided for the transmission of information on both edges of the clock signal, that is, twice per clock. This is where the abbreviation DDR - Double Data Rate - comes from.

Kingston DDR Memory Module

With the advent of the DDR standard, such concepts as real and effective memory frequency appeared. For example, many DDR memory modules ran at 200 MHz. This frequency is called real. But due to the fact that data transfer was carried out on both edges of the clock signal, manufacturers, for marketing purposes, multiplied this figure by 2 and obtained a supposedly effective frequency of 400 MHz, which was indicated in the labeling (in this case, DDR-400). At the same time, the JEDEC specifications indicate that using the term “megahertz” to characterize the level of memory performance is completely incorrect! Instead, "millions of transfers per second per data output" should be used. However, marketing is a serious matter, and few people were interested in the recommendations specified in the JEDEC standard. Therefore, the new term never took root.

Also in the DDR standard, a dual-channel memory mode appeared for the first time. It could be used if there was an even number of memory modules in the system. Its essence is to create a virtual 128-bit bus by interleaving modules. In this case, 256 bits were sampled at once. On paper, a dual-channel mode can double the performance of the memory subsystem, but in practice the speed increase is minimal and is not always noticeable. It depends not only on the RAM model, but also on timings, chipset, memory controller and frequency.

Four memory modules operate in dual-channel mode

Another innovation in DDR was the presence of a QDS signal. It is located on the printed circuit board along with the data lines. QDS was useful when using two or more memory modules. In this case, the data arrives at the memory controller with a slight time difference due to the different distances to them. This creates problems when choosing a clock signal for reading data, which QDS successfully solves.

As mentioned above, DDR memory modules were made in DIMM and SO-DIMM form factors. In the case of DIMMs, the number of pins was 184 pieces. In order for DDR and SDRAM modules to be physically incompatible, for DDR solutions the key (the cut in the pad area) was located in a different location. In addition, DDR memory modules operated at a voltage of 2.5 V, while SDRAM devices used a voltage of 3.3 V. Accordingly, DDR had lower power consumption and heat dissipation compared to its predecessor. The maximum frequency of DDR modules was 350 MHz (DDR-700), although JEDEC specifications only provided for a frequency of 200 MHz (DDR-400).

DDR2 and DDR3 memory

The first DDR2 modules went on sale in the second quarter of 2003. Compared to DDR, second-generation RAM has not received significant changes. DDR2 used the same 2n-prefetch architecture. If previously the internal data bus was twice as large as the external one, now it has become four times wider. At the same time, the increased performance of the chip began to be transmitted via an external bus at double the frequency. Precisely frequency, but not double transmission speed. As a result, we found that if the DDR-400 chip operated at a real frequency of 200 MHz, then in the case of DDR2-400 it operated at a speed of 100 MHz, but with twice the internal bus.

Also, DDR2 modules received a larger number of contacts for connection to the motherboard, and the key was moved to another location for physical incompatibility with SDRAM and DDR sticks. The operating voltage has been reduced again. While DDR modules operated at a voltage of 2.5 V, DDR2 solutions operated at a potential difference of 1.8 V.

By and large, this is where all the differences between DDR2 and DDR end. At first, DDR2 modules were characterized by high latencies, which made them inferior in performance to DDR modules with the same frequency. However, the situation soon returned to normal: manufacturers reduced latencies and released faster sets of RAM. The maximum DDR2 frequency reached an effective 1300 MHz.

Different key positions for DDR, DDR2 and DDR3 modules

The transition from DDR2 to DDR3 followed the same approach as the transition from DDR to DDR2. Of course, data transmission at both ends of the clock signal has been preserved, and the theoretical throughput has doubled. DDR3 modules retained the 2n-prefetch architecture and received 8-bit prefetch (DDR2 had 4-bit). At the same time, the internal tire became eight times larger than the external one. Because of this, once again, with the change of memory generations, its timings increased. The nominal operating voltage for DDR3 has been reduced to 1.5 V, making the modules more energy efficient. Note that, in addition to DDR3, there is DDR3L memory (the letter L means Low), which operates with a voltage reduced to 1.35 V. It is also worth noting that DDR3 modules turned out to be neither physically nor electrically compatible with any of the previous generations of memory.

Of course, DDR3 chips have received support for some new technologies: for example, automatic signal calibration and dynamic signal termination. However, in general, all changes are predominantly quantitative.

DDR4 - another evolution

Finally, we get to the brand new DDR4 memory. The JEDEC Association began developing the standard back in 2005, but only in the spring of this year the first devices went on sale. As stated in a JEDEC press release, during development, engineers tried to achieve the highest performance and reliability, while increasing the energy efficiency of the new modules. Well, we hear this every time. Let's see what specific changes DDR4 memory has received in comparison with DDR3.

In this picture you can trace the evolution of DDR technology: how the voltage, frequency and capacitance indicators changed

One of the first DDR4 prototypes. Oddly enough, these are laptop modules

As an example, consider an 8GB DDR4 chip with a 4-bit wide data bus. Such a device contains 4 groups of banks, 4 banks each. Inside each bank there are 131,072 (2 17) rows with a capacity of 512 bytes each. For comparison, you can give the characteristics of a similar DDR3 solution. This chip contains 8 independent banks. Each bank contains 65,536 (2 16) rows, and each row contains 2048 bytes. As you can see, the length of each line of a DDR4 chip is four times less than the length of a DDR3 line. This means that DDR4 scans banks faster than DDR3. At the same time, switching between the banks themselves also occurs much faster. Let us immediately note that for each group of banks there is an independent choice of operations (activation, read, write or regeneration), which allows increasing the efficiency and memory bandwidth.

The main advantages of DDR4: low power consumption, high frequency, large capacity of memory modules

Is DDR4. This is what current Intel processors support (although they also left partial support for DDR3). New motherboards for AMD processors will also be released for DDR4, which will appear in early 2017. This article will help you find out how to choose DDR4 for building or a new PC or upgrade, and how RAM for laptops differs from it.

Before choosing DDR4 memory, you need to familiarize yourself a little with the features of this type of RAM. Essentially, DDR4 memory is a surface-mount BGA (solder ball array) chip, which makes it universal for all types of electronics, from routers to servers. However, for ease of installation, as well as maintaining the possibility of upgrading, increasing the available amounts of RAM and overall unification, PCs usually use a modular design.

Format

DDR4 memory chips are soldered onto small boards, ranging from 4 to 16 pieces. Such boards are called DIMM (Double In-line Memory Module - double-sided memory module) and are equipped with 284 contacts. They have the same dimensions (5.25″ or a little more than 13 centimeters), but are physically incompatible with DDR3, since the latter’s DIMM module has 240 pins. In addition, the modules have different locations of a special key cutout that prevents the board from being installed on the wrong side or in an incompatible slot. DIMMs are the main type of RAM memory for desktop computers and servers.

For laptops with increased requirements for compactness, SO-DIMM modules (Small Outline DIMM - double-sided memory module with small pins) have been created. Also, similar boards are used in monoblocks, nettops and other types of compact personal computers. They are half the size of DIMMs (6.76 cm) and have only 260 pins.

Characteristics

The second criterion by which DDR4 memory can be classified is its performance characteristics. The main ones are clock speed (and the bandwidth directly related to it), latency and voltage.

Clock frequency and bandwidth characterize the performance of memory in sequential reading and writing mode. DDR4 RAM is available with support for frequencies from 1600 MHz (very rare in practice) to 3200 MHz. The most common frequencies at the moment are 1866 MHz (bandwidth - 12800 MB/s), 2133 MHz (17064 MB/s) and 2400 MHz (19200 MB/s). Most computers are designed to work with them.

CAS latency is the delay (measured in the number of working cycles) between submitting a request to read/write data and completing this operation. This parameter characterizes memory performance in random read/write mode. The lower the latency value, the more responsive the memory. At equal frequencies, the module with the lower delay duration (latency) will be faster.

Voltage— module supply voltage. At the moment, the only common value is 1.2 V. There is also LPDDR4 (low power DDR4) memory that uses lower voltages. It is not yet popular, and is used only in compact devices (ultrabooks, tablets, smartphones) that do not support its upgrade. The disadvantage of this type of memory is its reduced performance for the sake of efficiency.

Choosing DDR4 memory when building a new PC

Choosing DDR4 RAM for a computer that is being built from scratch is the easiest way. As of late 2016-early 2017, the only platform supporting this memory is Intel SkyLake (Core i3-i7 6xxx, Celeron and Pentium of this family). The base memory frequency for this platform is 2133 MHz. Higher frequencies are not supported by all boards and are only achieved during overclocking.

When purchasing a board equipped with two memory slots, it is advisable to purchase one large-capacity stick (8 or 16 GB). This will leave the possibility in the future to add another one to it and double the amount of RAM. For boards with four DIMM slots, you can choose a set of 2 smaller strips. In this case, the possibility of an upgrade remains, and the performance is at least slightly increased due to the dual-channel mode.

Heatsinks on DDR4 memory sticks are more a decorative element than a functional one. The power consumption of this generation of RAM is tiny (about 0.5-2 W), so there is no need for additional cooling. In a case with a transparent wall and backlight, heatsinks on the memory strips will decorate the inside of the PC. However, if the choice is between planks with the same parameters, and the aesthetic component fades into the background, there is no point in overpaying for radiators. They are really useful only for overclockers who overclock RAM much higher than factory frequencies.