So ddr. Modern types of memory DDR, DDR2, DDR3 for desktop computers


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 was support for the operational standard DDR memory 4.

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, it 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 capacity of the capacitors, it constantly requires updating. By the way, in addition to dynamic memory, there is also static memory, which does not require constant update data (SRAM). SRAM, for example, underlies 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 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, the speech is in this case It's about DIMMs. Devices made in the SO-DIMM form factor naturally have smaller number 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 established mass production 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 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 capacity 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 for execution a certain team. 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 the activation command and the 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. 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 performance random access memory. 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 printed circuit board along with 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 different distances before 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 delays and released more speed dials random access memory. 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 got to the perfect new memory DDR4 type. 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 amount of memory modules

Memory DDR3 is gradually losing its position as the most widespread and is no longer recommended for assembling new systems. It’s another matter if the task is to modernize a slightly outdated computer, and within a limited budget. It’s clear that such conditions exclude maximally overclocked memory kits from the list of options, and they are not considered in our review.

It is noteworthy that within the platform Intel The race for megahertz doesn't make much sense either. The exception here is quite specific tasks that are not of interest to most users. On the other hand, the difference in price for memory kits of the same size but with different clock frequencies is vanishingly small (in the range from 2133 to 3000 MHz, of course). So why not choose a faster set of RAM for the future?

The situation is completely different with the latest platform AMD. Due to the peculiarities of their internal architecture, the performance of Ryzen processors directly depends on the operating frequency of the Infinity Fabric memory bus, and therefore its controller. In turn, the frequency of the latter is “tied” to the characteristics installed modules and can be increased by overclocking.

An extremely unpleasant nuance in choosing memory modules for Ryzen The problem is that not every kit will work in such a system even at its rated clock frequency. Here the problem lies in the architecture of the modules themselves. Briefly, the recommendations can be boiled down to two tips: focus on peer-to-peer memory sticks and the latest BIOS revision for the motherboard. The newer the AGESA protocol is, the better. Keep in mind, dual-rank memory with Ryzen will always run at lower frequencies, and early versions The specified protocol is “friendly” only for modules built on Samsung chips. And not just any, but exclusively the B-Die generation.

Happy upgrade!

Hello, dear readers of the blog site. In one of the previous articles, I mentioned the differences between the two most common today - ddr2 and ddr3. There I said that in terms of performance and power consumption, ddr3 memory looks better than ddr2, which is already outdated by modern standards, but is the difference between them really that big? And is it worth buying ddr3 type RAM, or should I stick with ddr2?

Numbers are numbers, but the difference in characteristics on paper is not always noticeable in reality. I suspect that many readers still have old-style motherboards with ddr2 memory, and I would really not like to change the board because it does not support the newfangled ddr3. What can I say, I myself now have two 2 gigabyte sticks of DDR2.

But I was always worried about one question - if I now change the motherboard to another one that supports ddr3 memory, while the processor, video card, etc. (except for memory) remain the same, will there be at least some noticeable increase in the speed of the computer (in games, in everyday work)? So today we will try to answer this question.

And to begin with, I propose to consider what capabilities and features has each type of memory. So, regarding ddr2:

  • The maximum amount of such memory is 16 GB for serial motherboards, rarely - 32 GB for server boards.
  • The maximum frequency for this type of memory is 800 MHz; in very rare cases, there are models overclocked to 1066 MHz.
  • The power consumption of one strip is 1.8 V.
  • The latency of ddr2 is much lower than that of ddr3. The delay shows how much time has passed from the moment the data is requested until it is read from the memory module (how much time the memory spends on certain operations). The lower this value, the better.
  • Since the delay time of ddr2 is less, then at the same operating frequencies given memory will work faster than ddr3.
  • The maximum volume of a single stick is 8 GB, I have never seen more.

Now regarding DDR3:

  • The maximum amount of memory that can be installed on the motherboard is practically unlimited, from 64 GB and further into space. True, it is not entirely clear for what purpose so much RAM might be needed. For me personally comfortable work 4 GB is enough, even with a reserve.
  • Recently I came across one model in the Yandex market, costing about 10,000 rubles, with a frequency of 3000 MHz and a capacity of 8 GB. I think this is the limit; I have never seen higher frequency models.
  • The power consumption of a standard ddr3 is about 1.5 V. There are also modifications DDR3L and LPDDR3, their power consumption is 1.35 V and 1.2 V, respectively.
  • Due to the architecture features, ddr3 memory sticks have longer latencies than ddr2.
  • Since ddr3 has a longer latency, this type of memory will work slower at the same operating frequencies. Therefore, usually the operating frequencies of ddr3 are an order of magnitude higher than those of ddr2.
  • The maximum possible volume of one stick is 32 GB.

Remember, in the previous article (link at the beginning) I mentioned incompatibility these two types of memory? That is, you won’t be able to buy a ddr3 stick and insert it into a ddr2 slot. So, there are combined motherboards that have several slots for different types memory, however, there is one limitation - their simultaneous use is impossible, but I personally never understood why.

As you can see, the differences between ddr2 and ddr3 are quite significant. But this is on paper, but in reality it turns out something like this.

Here are the results of How does the type of RAM affect the number of FPS?(frames per second) in the game Crysis (the more frames the better), the graph is taken from a very well-known resource in the bourgeoisie: www.tweaktown.com/articles/1782/amd_phenom_ii_ddr2_vs_ddr3_performance/index11.html. At one time, this game could safely be called a breakthrough in terms of graphics and physics, naturally, it simply unrealistically loaded the processor-video card-RAM “combination”, so almost from the moment it came out, it began to be used as a benchmark - which translated from English means "performance test".

The graph shows that the increase was about 1-2 FPS, which, you see, is very modest. Okay, maybe it’s only Crysis that produced such results, maybe it will be different in other games? Here is a graph with test results for several games at once, taken from the site: www.ixbt.com/cpu/ddr2-800-vs-ddr3-1333.shtml.

And here there is no performance gain at all, as you may have noticed. But there must be a result somewhere, after all? Or have the marketers lied again, and ddr3 is of no use? Below are the results of the popular synthetic benchmark 3DMark Vantage. Synthetic benchmarks load the system components many times more than regular games, for example.

Even here the difference is minimal, it is so small that you can’t feel it. The same goes for games; you simply won’t notice a difference of 1-5 fps by eye. So what's the point of ddr3 then? I think not yet central processing units cannot fully utilize the speed capabilities of ddr3, perhaps this will happen in the near future, and then ddr2 will completely go off the market and everyone will forget about it. In the meantime, for those of you who still use ddr2 memory for some reason, I do not recommend changing it to a more modern one, because the use of this is like milk from a goat.

Another thing is that now almost everything motherboards They are equipped with ddr3 connectors, so you won’t have to choose. At the moment, ddr3 memory is already cheaper than the outdated ddr2 (for the same money you can buy ddr3 memory with a capacity 2 times larger), so owners of old mat. motherboards, there are two options to choose from - either pay at double the rate, or buy a new motherboard with a new processor, which looks like a much more unprofitable solution compared to the first option. When RAM is not widely available on sale, it becomes more expensive. Thank you.

There are several common types of memory modules used in modern computers and computers released several years ago, but still working in homes and offices.
For many users, they can be distinguished by both appearance, and in terms of performance - this is a big problem.
In this article we will look at the main features of different memory modules.

FPM

FPM (Fast Page Mode) is a type of dynamic memory.
Its name corresponds to the principle of operation, since the module allows faster access to data that is on the same page as the data transferred during the previous cycle.
These modules were used on most computers with 486 processors and in early systems With Pentium processors, approximately in 1995.

EDO

EDO (Extended Data Out) modules appeared in 1995 as new type memory for computers with Pentium processors.
This is a modified version of FPM.
Unlike its predecessors, EDO starts sampling next block memory at the same time it sends the previous block to the central processor.

SDRAM

SDRAM (Synchronous DRAM) is a type of random access memory that works so fast that it can be synchronized with the processor frequency, excluding standby modes.
The microcircuits are divided into two blocks of cells so that while accessing a bit in one block, preparations are in progress for accessing a bit in another block.

If the time to access the first piece of information was 60 ns, all subsequent intervals were reduced to 10 ns.
Since 1996, the majority Intel chipsets began to support this type of memory module, making it very popular until 2001.

SDRAM can operate at 133 MHz, which is almost three times faster than FPM and twice as fast as EDO.
Most computers with Pentium and Celeron processors released in 1999 used this type of memory.

DDR

DDR (Double Data Rate) was a development of SDRAM.
This type of memory module first appeared on the market in 2001.
The main difference between DDR and SDRAM is that instead of doubling clock frequency to speed up operation, these modules transmit data twice in one clock cycle.
Now this is the main memory standard, but it is already beginning to give way to DDR2.

DDR2

DDR2 (Double Data Rate 2) is a newer variant of DDR that should theoretically be twice as fast.
DDR2 memory first appeared in 2003, and chipsets supporting it appeared in mid-2004.

This memory, like DDR, transfers two sets of data per clock cycle.
The main difference between DDR2 and DDR is the ability to operate at significantly higher clock speeds, thanks to improvements in design.
But the modified operating scheme, which makes it possible to achieve high clock frequencies, at the same time increases delays when working with memory.

DDR3

DDR3 SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory, Third Generation) is a type of random access memory used in computer technology as RAM and video memory.
It replaced DDR2 SDRAM memory.

DDR3 has a 40% reduction in energy consumption compared to DDR2 modules, which is due to the lower (1.5 V, compared to 1.8 V for DDR2 and 2.5 V for DDR) power supply voltage of the memory cells.
Reducing the supply voltage is achieved through the use of a 90-nm (initially, later 65-, 50-, 40-nm) process technology in the production of microcircuits and the use of Dual-gate transistors (which helps reduce leakage currents).

DIMMs with DDR3 memory are not mechanically compatible with the same DDR2 memory modules (the key is located in a different location), so DDR2 cannot be installed in DDR3 slots (this is done to prevent the mistaken installation of some modules instead of others - these types of memory are not the same according to electrical parameters).

RAMBUS (RIMM)

RAMBUS (RIMM) is a type of memory that appeared on the market in 1999.
It is based on traditional DRAM, but with a radically changed architecture.
The RAMBUS design makes memory access more intelligent, allowing pre-access to data while slightly offloading the CPU.

The main idea used in these memory modules is to receive data in small packages, but at a very high clock frequency.
For example, SDRAM can transfer 64 bits of information at 100 MHz, and RAMBUS can transfer 16 bits at 800 MHz.
These modules did not become successful as Intel had many problems with their implementation.
RDRAM modules appeared in game consoles Sony Playstation 2 and Nintendo 64.


Translation: Vladimir Volodin

My respects dear site visitors. In the last article I wrote about. Now, having learned what it is and what and how it serves, many of you are probably thinking about purchasing a more powerful and productive RAM for your computer. After all, increasing computer performance with additional memory RAM is the simplest and cheapest (unlike, for example, a video card) method of upgrading your pet.

And... Here you are standing at the display case with packages of RAMs. There are many of them and they are all different. Questions arise: Which RAM should I choose?How to choose the right RAM and not make a mistake?What if I buy a RAM and then it doesn’t work? These are completely reasonable questions. In this article I will try to answer all these questions. As you already understand, this article will take its rightful place in the series of articles in which I wrote about how to choose the right individual components computer i.e. iron. If you haven't forgotten, it included the following articles:
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This cycle will continue, and in the end you will be able to assemble for yourself a super computer that is perfect in every sense 🙂 (if finances allow, of course :))
In the meantime learning how to choose the right RAM for your computer.
Go!

RAM and its main characteristics.

When choosing RAM for your computer, you must take into account your motherboard and processor because RAM modules are installed on the motherboard and it also supports certain types of RAM. This creates a relationship between motherboard, processor and RAM.

Find out about what RAM does your motherboard and processor support? You can go to the manufacturer’s website, where you need to find the model of your motherboard, as well as find out which processors and RAM it supports. If you don’t do this, it will turn out that you bought a super modern RAM, but it is not compatible with your motherboard and will gather dust somewhere in your closet. Now let's move directly to the main technical characteristics of RAM, which will serve as unique criteria when choosing RAM. These include:

Here I have listed the main characteristics of RAM that you should pay attention to first when purchasing it. Now we will reveal each of them in turn.

Type of RAM.

Today, the most preferred type of memory in the world is memory modules DDR(double data rate). They differ in release time and, of course, technical parameters.

  • DDR or DDR SDRAM(translated from English: Double Data Rate Synchronous Dynamic Random Access Memory - synchronous dynamic memory with random access and double data transfer rate). Modules of this type have 184 contacts on the strip, are powered by a voltage of 2.5 V and have a clock frequency of up to 400 megahertz. This type RAM is already obsolete and is used only in old motherboards.
  • DDR2- widespread in given time memory type. It has 240 contacts on the printed circuit board (120 on each side). Consumption, unlike DDR1, is reduced to 1.8 V. The clock frequency ranges from 400 MHz to 800 MHz.
  • DDR3- the leader in performance at the time of writing this article. It is no less common than DDR2 and consumes 30-40% less voltage compared to its predecessor (1.5 V). Has a clock frequency of up to 1800 MHz.
  • DDR4- a new, super modern type of RAM, ahead of its counterparts both in performance (clock frequency) and voltage consumption (and therefore characterized by lower heat generation). Support for frequencies from 2133 to 4266 MHz is announced. On this moment These modules have not yet entered mass production (they promise to release them into mass production in mid-2012). Officially, fourth generation modules operating in DDR4-2133 at a voltage of 1.2 V were presented at CES, by Samsung January 04, 2011.

Amount of RAM.

I won’t write much about memory capacity. Let me just say that it is in this case that size matters :)
Just a few years ago, RAM of 256-512 MB satisfied all the needs of even cool gaming computers. Currently for normal functioning separately only to the operating room windows systems 7 requires 1 GB of memory, not to mention applications and games. There will never be too much RAM, but I’ll tell you a secret that 32-bit Windows uses only 3.25 GB of RAM, even if you install all 8 GB of RAM. You can read more about this.

Dimensions of the planks or the so-called Form factor.

Form - factor- these are the standard sizes of RAM modules, the type of design of the RAM strips themselves.
DIMM(Dual InLine Memory Module - a double-sided type of module with contacts on both sides) - mainly intended for desktop desktop computers, and SO-DIMM used in laptops.

Clock frequency.

This is pretty important technical parameter random access memory. But the motherboard also has a clock frequency and it is important to know operating frequency buses of this board, because if you bought, for example, a RAM module DDR3-1800, and the motherboard slot (connector) supports the maximum clock frequency DDR3-1600, then the RAM module as a result will operate at a clock frequency of 1600 MHz. In this case, all sorts of failures, errors in the operation of the system, etc. are possible.

Note: Memory bus frequency and processor frequency are completely different concepts.

From the tables above, you can understand that the bus frequency, multiplied by 2, gives the effective memory frequency (indicated in the “chip” column), i.e. gives us the data transfer speed. The name tells us the same thing. DDR(Double Data Rate) - which means double the data transfer rate.
For clarity, I will give an example of decoding in the name of the RAM module - Kingston/PC2-9600/DDR3(DIMM)/2Gb/1200MHz, Where:
—Kingston- manufacturer;
- PC2-9600— name of the module and its capacity;
- DDR3(DIMM)— memory type (form factor in which the module is made);
— 2Gb— module volume;
- 1200MHz— effective frequency, 1200 MHz.

Bandwidth.

Bandwidth- a memory characteristic on which system performance depends. It is expressed as the product of frequency system bus on the amount of data transmitted per clock cycle. Throughput (peak data rate) is a comprehensive measure of capability RAM, it takes into account transmission frequency, bus width and the number of memory channels. The frequency indicates the potential of the memory bus per clock cycle - at a higher frequency, more data can be transferred.
The peak indicator is calculated using the formula: B=f*c, Where:
B is the bandwidth, f is the transmission frequency, c is the bus width. If you use two channels to transmit data, we multiply everything received by 2. To get a figure in bytes/s, you need to divide the result by 8 (since there are 8 bits in 1 byte).
For better performance RAM bus bandwidth And processor bus bandwidth must match. For example, for a processor Intel core 2 duo E6850 with a system bus of 1333 MHz and a bandwidth of 10600 Mb/s, you can install two modules with a bandwidth of 5300 Mb/s each (PC2-5300), in total they will have a system bus bandwidth (FSB) equal to 10600 Mb/s s.
Bus frequency and bandwidth are denoted as follows: “ DDR2-XXXX" And " PC2-YYYY". Here "XXXX" denotes the effective memory frequency, and "YYYY" the peak bandwidth.

Timings (latency).

Timings (or latency) are the time delays of the signal, which, in technical specifications RAM is written as " 2-2-2 " or " 3-3-3 " etc. Each number here expresses a parameter. In order it is always " CAS Latency"(working cycle time), " RAS to CAS Delay" (time full access) And " RAS Precharge Time» (pre-charge time).

Note

So that you can better understand the concept of timings, imagine a book, it will be our RAM that we access. Information (data) in a book (RAM) is distributed among chapters, and chapters consist of pages, which in turn contain tables with cells (as in Excel tables). Each cell with data on the page has its own vertical (columns) and horizontal (rows) coordinates. To select a row, the RAS (Raw Address Strobe) signal is used, and to read a word (data) from the selected row (i.e., to select a column), the CAS (Column Address Strobe) signal is used. Full cycle reading begins with the opening of the “page” and ends with its closing and recharging, because otherwise the cells will be discharged and the data will be lost. This is what the algorithm for reading data from memory looks like:

  1. the selected "page" is activated by applying the RAS signal;
  2. data from the selected line on the page is transmitted to the amplifier, and a delay is required for data transmission (it is called RAS-to-CAS);
  3. a CAS signal is given to select a (column) word from that row;
  4. data is transferred to the bus (from where it goes to the memory controller), and a delay also occurs (CAS Latency);
  5. the next word comes without delay, since it is contained in the prepared line;
  6. after access to the row is completed, the page is closed, the data is returned to the cells and the page is recharged (the delay is called RAS Precharge).

Each number in the designation indicates how many bus cycles the signal will be delayed. Timings are measured in nanoseconds. The numbers can have values ​​from 2 to 9. But sometimes a fourth one is added to these three parameters (for example: 2-3-3-8), called “ DRAM Cycle Time Tras/Trc” (characterizes the performance of the entire memory chip as a whole).
It happens that sometimes a cunning manufacturer indicates only one value in the RAM characteristics, for example “ CL2"(CAS Latency), the first timing is equal to two clock cycles. But the first parameter does not have to be equal to all timings, and may be less than others, so keep this in mind and do not fall for the manufacturer’s marketing ploy.
An example to illustrate the impact of timings on performance: a system with memory at 100 MHz with 2-2-2 timings has approximately the same performance as the same system at 112 MHz, but with 3-3-3 timings. In other words, depending on latency, the performance difference can be as much as 10%.
So, when choosing, it is better to buy memory with the lowest timings, and if you want to add a module to an already installed one, then the timings of the purchased memory must match the timings of the installed memory.

Memory operating modes.

RAM can operate in several modes, if of course such modes are supported by the motherboard. This single channel, two-channel, three-channel and even four-channel modes. Therefore, when choosing RAM, you should pay attention to this module parameter.
Theoretically, the speed of operation of the memory subsystem in dual-channel mode increases by 2 times, in three-channel mode - by 3 times, respectively, etc., but in practice, in dual-channel mode, the performance increase, unlike single-channel mode, is 10-70%.
Let's take a closer look at the types of modes:

  • Single channel mode(single-channel or asymmetric) – this mode is activated when only one memory module is installed in the system or all modules differ from each other in memory capacity, operating frequency or manufacturer. It doesn’t matter what slots or memory you install into. All memory will run at the speed of the slowest memory installed.
  • Dual Mode(dual-channel or symmetrical) - the same amount of RAM is installed in each channel (and theoretically the maximum data transfer rate is doubled). In dual-channel mode, memory modules work in pairs: 1st with 3rd and 2nd with 4th.
  • Triple Mode(three-channel) – the same amount of RAM is installed in each of the three channels. Modules are selected according to speed and volume. To enable this mode, modules must be installed in slots 1, 3 and 5/or 2, 4 and 6. In practice, by the way, this mode is not always more productive than the two-channel one, and sometimes even loses to it in data transfer speed.
  • Flex Mode(flexible) – allows you to increase the performance of RAM when installing two modules of different sizes, but the same operating frequency. As in dual-channel mode, memory cards are installed in the same connectors of different channels.

Generally, the most common option is dual-channel memory mode.
To operate in multi-channel modes, there are special sets of memory modules - the so-called Kit memory(Kit set) - this set includes two (three) modules, from the same manufacturer, with the same frequency, timings and memory type.
Appearance of KIT kits:
for dual channel mode

for three-channel mode

But the most important thing is that such modules are carefully selected and tested by the manufacturer itself to work in pairs (triples) in two- (three-) channel modes and do not imply any surprises in operation and configuration.

Manufacturer of modules.

Now on the market RAM Such manufacturers as have proven themselves well: Hynix, amsung, Corsair, Kingmax, Transcend, Kingston, OCZ…
Each company has its own for each product marking number, from which, if deciphered correctly, you can find out a lot of useful information about the product. Let's try to decipher the module marking as an example Kingston families ValueRAM(see image):

Explanation:

  • KVR– Kingston ValueRAM i.e. manufacturer
  • 1066/1333 – operating/effective frequency (Mhz)
  • D3- memory type (DDR3)
  • D (Dual) – rank/rank. A dual-rank module is two logical modules soldered onto one physical channel and alternately using the same physical channel (needed to achieve the maximum amount of RAM when limited quantities slots)
  • 4 – 4 DRAM memory chips
  • R – Registered, indicates stable operation without failures or errors for as long a continuous period of time as possible
  • 7 – signal delay (CAS=7)
  • S– temperature sensor on the module
  • K2– set (kit) of two modules
  • 4G– the total volume of the kit (both slats) is 4 GB.

Let me give you another example of marking CM2X1024-6400C5:
From the labeling it is clear that this is DDR2 module volume 1024 MB standard PC2-6400 and delays CL=5.
Stamps OCZ, Kingston And Corsair recommended for overclocking, i.e. have the potential for overclocking. They will have small timings and a clock frequency reserve, plus they are equipped with radiators, and some even coolers for heat removal, because When overclocking, the amount of heat increases significantly. The price for them will naturally be much higher.
I advise you not to forget about fakes (there are a lot of them on the shelves) and buy RAM modules only in serious stores that will give you a guarantee.

Finally:
That's all. With the help of this article, I think you will no longer be mistaken when choosing RAM for your computer. Now you can choose the right RAM for the system and increase its performance without any problems. Well, for those who will buy RAM (or have already bought it), I will dedicate the following article, in which I will describe in detail how to install RAM correctly into the system. Do not miss…


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