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RAM - Random Access Memory - How to Choose the Right Kind of RAM Memory for Your Computer - Page 1

Last updated on 16 April 2008

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RAM is an acronym for Random Access Memory that is also known as volatile memory, because the data it holds is lost when the desktop PC or laptop/notebook computer using it is switched off. Briefly, RAM memory is used by the system to store data in the form of files for processing by a computer's central processing unit (CPU), also known as the processor. The processors used in most PCs are made by Intel and AMD. The processor runs the program and data files according to instructions given to it by the operating system, which, on PCs, is usually a version of Windows, or, to a much lesser extent, a version of Linux.

The amount of RAM memory used in modern computers is expressed in megabytes (MB) and gigabytes (GB). A gigabyte (1GB) is 1024MB. Most new desktop and laptop computers that come with Windows Vista preinstalled should have a minimum of 2GB or RAM memory.

The RAM memory used in current PCs comes in the form of DDR and DDR2 and DDR3 memory modules, and example of which is shown in the image below.

Unless all of the memory slots on a computer's motherboard are already fitted with memory modules, the RAM memory in most desktop and laptops computers can be increased by installing more memory (upgrading the memory). Installing one or more additional memory modules in a desktop or a laptop computer is a simple process that is dealt with at the top of Page 2 of this article.

Most current (December 2007) desktop PCs and laptop PCs have motherboards that use DDR or DDR2 memory. However, DDR3 memory is now available, so, as time goes on, more motherboards will be using it.

The modules are installed in the DIMM memory slots on the PC's motherboard. Most motherboards provide four DIMM slots, but some micro-ATX motherboards only have two slots, both of which must be filled if the memory is used in the fastest dual-channel mode.

MSI K8N Diamond Plus Socket 939 motherboard shown above has four DIMM slots that are in the bottom right hand side of the board (when the connection ports can be seen at the top of the board). On this motherboard, the slots are alternatively coloured blue and teal green to make it easier to install the modules in dual-channel or single-channel modes, the instructions for which are provided in the motherboard's user manual that comes with it, or which can be downloaded from MSI's website.

When updgrading memory, it is essential that you purchase the right type of memory module, because DDR, DDR2, and DDR3 memory is incompatible with each other. You cannot use a DDR2 module in a DDR DIMM slot, etc. However, some motherboards can have slots for both DDR/DDR2 or DDR2/DDR3 modules. No motherboard support all three types. A DDR3-supporting motherboard will not support DDR memory. The motherboard's manual or the PC's user guide should provide the information required to be able to tell which type of slots are provided.

If you don't have a copy of the manual, you should be able to download one in the PDF format from the manufacturer's website. You can use a tool called CPU-Z to find out the make/model of the motherboard as well as the type of memory installed, the size of the module(s), and which modules are installed in which slots. Note that a PDF reader, such as the free Foxit Reader is required to read PDF documents.

Most DDR/DDR2/DDR3 memory comes in matched pairs of modules to take advantage of dual-channel mode. Modern motherboards have a dual-channel memory bus, which makes it possible for pairs of modules to have a performance advantage compared to using a single module of the same size. In other words, two 1GB modules in dual-channel mode outperform a single 2GB module that can only operate in single-channel mode.

More information on single-channel and dual-chanel modes of operation of DDR/DDR2/DDR3 memory is provided futher on in this article.

Visit the Desktop PCs section of this site for information on how to buy, build, repair, fix, and protect the various types of desktop PCs.

Visit the Laptop/Notebook PCs section of this site for information on buying and protecting them, and fixing problems with them.

Adding additional memory requires making use of free DIMM slots, so, if you are buying a brand-name PC, it is advisable to find out if additional memory can be installed. This is advisable because the amount of memory used by Microsoft's Windows operating system has been increasing with each new version since Windows 95 and Windows 98, which could run comfortably on 32MB and 64MB respectively.

A computer running Windows XP Home Edition that doesn't run memory-hungry applications, such as video-editing software, should have minimum of 512MB of RAM memory to run comfortably. Such a computer will run ordinary office applications, etc., with 256MB of memory, but slowly. Motherboard user manuals recommend that the 32-bit versions of Windows XP Home and Professional Editions should have less than 3GB of memory installed, because they don't support more than that amount of memory. The 64-bit version of Windows XP Professional supports a maximum of 8GB of memory.

Most of the versions of Windows Vista require more RAM memory to run optimally (on a computer that doesn't use memory-hungry applications) than Windows XP. A video-editing application is an example of memory-intensive software. Only Windows Vista Home Basic has a recommended minimum amount of memory of 512MB, which is the same minimal amount recommended for Windows XP. Windows Vista Home Premium, the most popular version, and Windows Vista Ultimate require a minimum of 1GB (1024MB) of memory, which is twice the minimal amount of memory recommended to run Windows XP. You should not install more than 3GB of memory in a PC running a 32-bit version of Windows Vista.

If you want to install 4GB or more of RAM, the computer must have a 64-bit processor, which almost all new computers now have. You can find out if a particular Intel or AMD processor is 32-bit or 64-bit on the following two pages:

Desktop CPU Comparison Guide - AMD processors -

http://www.techarp.com/showarticle.aspx?artno=337&pgno=0

Desktop CPU Comparison Guide - Intel processors -

http://www.techarp.com/showarticle.aspx?artno=337&pgno=4

The computer must also be running a 64-bit operating system, which could be the latest versions of Linux, or the 64-bit versions of Windows XP Professional (XP Home Edition only comes as a 32-bit version), or the 64-bit versions of Windows Vista, which are:

Windows Vista Enterprise 64-bit edition • Windows Vista Home Basic 64-bit edition • Windows Vista Home Premium 64-bit edition • Windows Vista Ultimate 64-bit edition • Windows Vista Business 64-bit edition

64-bit Editions of Windows Vista -

http://www.microsoft.com/windows/products/windowsvista/editions/64bit.mspx

Vista Workshop – Performance Boost with 8GB of RAM -

"In order to be able to utilize the entire [8GB of] system memory, you will therefore need to use a 64 bit version of Windows Vista. In this article, we will take a look at memory usage under the 32 and 64 bit versions of Windows Vista and analyze how the operating system behaves with different amounts of RAM." -

http://www.tomshardware.co.uk/Microsoft-Windows-Vista,review-30272.html

Note well that the 32-bit versions of Windows Vista will recognise less than 4GB of memory unless the computer meets certain requirements.

"How much memory your Windows OS will recognize depends on which version of Windows you are running. 32-bit versions of Windows will see (and utilize) only 3GB or 3.5GB. To utilize more memory, install a 64-bit version of your OS. More information about OS memory maximums can be found at http://www.crucial.com/kb/answer.aspx?qid=4251."

Read this MS Knowledge Base article for more information:

The system memory that is reported in the System Information dialog box in [a 32-bit version of] Windows Vista is less than you expect if 4 GB of RAM is installed -

http://support.microsoft.com/kb/929605

Read this Q&A on this site for more information on Vista's RAM requirements: The memory requirements of Windows Vista: How much RAM memory does Windows Vista really need to run optimally?

Kingston Technology - Ultimate Memory Guide -

Covers Windows Vista, Windows XP, Windows 2000, Windows 98, Linux, and Macintosh OS X. - http://www.kingston.com/tools/umg/umg01b.asp

Buying a new PC? 'Windows Vista Capable' barely hits the mark - IBM'er says Vista's RAM sweet spot is 4GB -

http://www.computerworld.com/action/...articleId=9011523&intsrc=hm_list

Note that the way in which Windows Vista uses virtual memory, which simulates RAM memory by using storage space on a PC's hard drive when actual memory runs low, has been improved.

Windows Vista: SuperFetch and External Memory Devices -

"Windows Vista sports a new memory performance enhancement system called SuperFetch and a new way to extend the virtual memory by way of External Memory Devices (EMD)." - http://articles.techrepublic.com.com/5100-10877_11-6039379.html?tag=nl.e132

For more information on this subject, read Windows Vista recommended system requirements.

Indeed, most of the current desktop PCs and laptop/notebook computers that are being sold new with Windows XP come with 1GB of RAM memory in anticipation of being upgraded to Windows Vista Home Premium or Windows Vista Ultimate. If you want to upgrade such a computer without having to upgrade the memory, it is advisable not to buy a computer unless it has at least that amount of memory.

Visit the Using Windows Vista section of this site for more information on the different versions of the new operating system.

Fortunately upgrading a computer's RAM is a relatively easy matter provided that the computer has one or more spare DIMM memory slots on its motherboard and you obtain the correct kind of DIMM module(s).

If a computer's motherboard only has two DIMM slots that each have a 256MB module installed in it, making a total of 512MB of memory, you can still upgrade the system to 1GB of memory if the motherboard supports 512MB modules in each slot (512 x 2 = 1024MB = 1GB of memory). You could then sell the two 256MB modules on an auction site such as eBay.

There are some other issues that you should know about, such as running DDR, DDR2, and DDR3 RAM in single-channel and dual-channel modes, so read the information in this article to make sure that you buy the correct memory for your computer's motherboard or brand-name PC.

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People are constantly complaining in newsgroups that they have purchased RAM that is not recognised at all by their computers, or is recognised as only a half, or even a quarter of its actual capacity. Usually, the RAM is not at fault, but is just incompatible with the computer's motherboard.

The problem arises because new types of RAM modules are introduced, and the older motherboard chipsets are not designed to recognise them.

A particular motherboard will have been designed to run the range of RAM modules that were on the market when it was released, but its manufacturer cannot anticipate changes in technology in its design, consequently the motherboard's manual will only list the types of RAM that the motherboard supports at the time it was made available.

Unfortunately, very few motherboard manufacturers update their manuals to report incompatibilities with types of RAM modules that were not available when the motherboard was released.

That is why you're advised to try using the relevant Crucial Memory Advisor in order to make sure that you don't purchase RAM that isn't supported by your brand-name computer or the computer's motherboard. Indeed, if you're contemplating buying a new motherboard, it would be a good idea to find out if it's listed by Crucial (or will be listed) before you buy it

The US and UK Memory Advisors (below) allow you to find out what types of RAM are available for your notebook computer, brand-name PC, or motherboard - and what the current prices are in the USA and the UK.

For example, if your computer has an Asus motherboard, open the menu, scroll down to Asus, and click GO. If, say, you have a Dell computer, scroll down to DELL, and do likewise. You will be taken to the relevant information on Crucial's website. Using MSI (Microstar) as an example, because it manufactures all kinds of computer equipment, on Crucial's website, you will have to choose which MSI product you require memory for - a motherboard, a desktop PC, or a laptop computer.

If a particular manufacturer isn't listed in the UK Memory Advisor, try looking for it in the US Memory Advisor, and vice versa. All you have to do is find out what the reference number is for a particular type and memory size of RAM that the system or motherboard supports and then order it from the US or UK site. Both sites will be able to supply all of the different kinds of RAM that Crucial sells, but one site might not list a particular make and model of computer or motherboard that the other site does list.

If you don't know the make and model of the motherboard installed in your computer, here is a good free utility - Belarc Advisor - that creates an analysis of the hardware and software on a personal computer. Look under FREE DOWNLOAD - http://www.belarc.com/. Another free utility that also provides detailed information on the memory itself is CPU-Z.

Crucial's UK and US Memory Advisors

Paul Mullen, the highly-respected computer guru of the Helpfile at ComputerShopper.co.uk - "I have recently been buying my memory only from Crucial Technology. I would rather pay the extra cost than waste time trying to track down the obscure program faults that bad memory can cause."

Up to a point, increasing the amount of RAM in a system can deliver very noticeable performance gains, but increasing it over that point usually delivers ever decreasing performance gains.

For example, in performance tests on a particular computer, if 256MB of RAM is sufficient to run all of the benchmark tests, increasing it to 512MB and then 1024MB (1GB) of RAM only produces performance gains of about 8% for each addition. In short, an increase of 256MB and then of 512MB of RAM both produce performance gains of 8% - a decrease of the gain in performance.

However, when the same system's RAM was increased from an insufficient 128MB of RAM to the 256MB that could run all of the tests, the overall performance gain of about 20% exceeded the threshold of 10% that Intel's research determined is necessary for the difference to become noticeable.

That said, performance gains are not the only benefit of increasing the amount of RAM in a computer, because, assuming there is sufficient hard disk drive space, the more RAM a system has, the bigger the programs it can run, and the more programs it can have loaded to run at the same time.

Note, however, that Windows 95, 98, and Me (Windows 9x) have limited System Resources that limit the number of programs that those versions of Windows can run at the same time. Windows keeps track of them via two 64KB blocks of memory (128KB) within the 640KB of Conventional RAM memory used by DOS.

Windows XP, Windows 2000, and Windows Vista don't have problems with what are known as System Resources, but the Windows 9x versions of Windows can crash or require that the system is restarted if they reach too low a level.

A four-part series on System Resources in Windows 9x - what they are, why they are unrelated to the amount of RAM, how to manage them and prevent memory leaks, etc. - is available here:

http://content.techweb.com/winmag/columns/explorer/2000/14.htm

What is RAM memory and what does it do?

RAM memory stores the data in electronic memory cells that are arranged in grids in much the same way as cells are arranged in a spreadsheet, from which data, in the binary form of ones and zeros, can be accessed and transferred at random to the processor for processing by the system's software.

The RAM is conventionally controlled by the memory controller of the motherboard's chipset, or, as is now also the case with the AMD Athlon 64 processors, by a memory controller built into the processor itself, which is capable of running DDR SDRAM and DDR2 SDRAM in single-channel mode and in the faster dual-channel mode. More information on DDR and DDR2 memory is provided further on in this article.

If the memory controller is built into the processor, the motherboard that runs the processor won't have a memory controller in its chipset.

The memory controller on a motherboard resides in a chip called the north bridge.

If the motherboard supports dual-channel DDR mode, and it also has an integrated graphics engine, the system performance will be boosted because integrated video uses system RAM, and RAM running in dual-channel mode is 5% to 10% faster than DDR RAM running in single-channel mode.

The data stored in a hard disk drive (HDD) cannot be accessed at random. Whole sectors, containing blocks of data, are transferred from a hard disk drive, placed in a large swap file on the same drive, and only then are selected files transferred to RAM for random access by the processor, which is itself only performing the instructions of the system's operating system (usually Windows), and its application software.

When the computer is turned off, all of the data in the RAM memory is lost, hence its alternative name of volatile memory, whereas all of the data on a hard disk drive is retained permanently until it is intentionally erased or overwritten by other software or stored data.

Apart from making use of a source of information such as one of the Crucial Memory Advisors at the top of this page to choose the correct type of memory, the motherboard (or mainboard) manual - that should be provided with a new or a second-hand PC - will provide all of the details about the different types of supported RAM, and the various combinations of modules per bank for each type that can be successfully installed.

There are many flavours of one type of RAM - with or without error checking (ECC), buffered or unbuffered, and several types of RAM - SDRAM, RDRAM, DDR RAM, etc., but at the moment, two kinds of the most commonly used type - DDR RAM (Double-Data-Rate) - is run by recent and the latest motherboards in the form of DIMM modules - standard density and double-density modules - with the latter kind being the latest development.

The module of DDR RAM can be single-sided (standard DDR) with memory chips on one side of the module only, or double-sided (double-density) with memory chips on both sides of the module.

Moreover, DDR RAM modules used as single-channel or dual-channel modules only differ in the way that the memory is accessed. Modules used in single-channel mode are accessed individually, but modules used in dual-channel mode are installed in pairs and use circuitry on the motherboard that allows them to be accessed at the same time, thereby effectively doubling their access speed.

Note that currently the highest official FSB (front side bus) speed/frequency used by both Intel Pentium 4 and AMD Athlon motherboards is 200MHz, even though the highest official effective RAM speed/frequency is 800MHz when using two modules of DDR400 RAM in dual-channel mode, each module of which works at an effective speed of 400MHz, but combine to make an effective speed of 800MHz.

Click here! to go to more detailed technical information on the relationship between DDR RAM and the FSB further down this page. Use your browser's Back button to return to this point on the page.

In other words, DDR (Double Data Rate) dual-channel RAM can effectively work at four times the speed of ordinary SDRAM were it able to function properly on an FSB of 200MHz. But SDRAM is only made to run on an FSB of 133MHz at an official maximum frequency of 133MHz, but it is used as the basis on which to determine the effective running speed of the new dual-channel DDR RAM using a particular FSB.

In other words, it is an effective speed increase over the speed of the FSB, because the DDR RAM is not actually running at 400MHz or 800MHz, it is running at the FSB of 200MHz, but is using RAM technology to access data at speeds which would be equivalent to using FSBs of 400MHz (DDR) and 800MHz (DDR running in dual-channel mode).

Note that the new AMD Athlon 64 FX processors run DDR RAM in dual-channel mode, but the standard Athlon 64 processors, which use a Socket 754 motherboard, can only run it in single-channel mode. Only the Athlon 64 and 64 FX processors that run on a Socket 939 and Socket AM2 motherboard can run the DDR (Socket 939) and DDR2 (Socket AM2) memory in dual-channel mode. Intel Pentium 4 processors can only use DDR or DDR2 RAM in dual-channel mode if the motherboard's chipset supports that mode, because unlike the Socket 939 and Socket AM2 Athlon 64 processors, they don't have a built-in memory controller.

At present, because of current restrictive system bottlenecks, the faster mode of operation of DDR RAM (dual-channel mode) doesn't offer much in the way of a performance boost over its forerunner - DDR RAM running in single-channel mode.

With all of the Athlon 64 processors, the memory (RAM) controller is now built into the processor instead of being controlled by the memory controller of the chipset on the motherboard. This means that there is less delay when the processor writes and reads to and from the RAM. HyperTransport links also connect the processor directly to the AGP and other input/output buses. This all means that the Athlon 64 processors have far fewer system bottlenecks that hamper system performance.

Therefore, in this case, the type of processor determines which mode of operation the system RAM can run in, as well as the motherboard. It used to be that only the motherboard's chipset determined the type of RAM, (or, in the case of dual-channel support, its mode of operation) that a system can run.

For more information on the AMD Athlon 64 processors, visit the Processors pages on this site.

Not all motherboards can use the double density type of RAM (which has memory chips on both sides of the module), and so will only be able to read the chips on one side if you install double-sided modules (a 256MB module will typically only register as 128MB with the BIOS setup program and Windows), so always make sure that the RAM you want to buy as an upgrade is compatible with the motherboard. It's always a sure sign that the motherboard does not support the type of RAM installed if it is not all recognised by the BIOS when it shows the memory count as the computer starts up.

Note that the amount of RAM is actively counted when the system boots (visit the BIOS page on this site to see images of start-up screens showing the memory count), and is reported on the General tab of the System Properties windows in a Windows 95/98/Me/XP system that is accessed via System in the Control Panel, or by entering msinfo32 in the Start => Run box to bring up the System Information window.

In Windows Vista, open System Properties by opening the Control Panel and clicking System and Maintenance => System. To access System Information in Windows Vista, you enter msinfo32 in the Start => Start Search box.

Asynchronous and Synchronous DRAM

Whether RAM is asynchronous or synchronous is a technical specification that doesn't have to be known in order to make a correct purchase decision, because other specifications are used to determine the type and flavour of RAM. For more information on this subject, visit this page:

http://www.pcguide.com/ref/ram/timingAsynch-c.html

Until motherboards with chipsets able to use DDR RAM became available , Intel's Pentium 4 processors could only use Rambus RDRAM, which runs at effective speeds of 400MHz and 800MHz (the 800MHz kind is dual-channel RDRAM), and is comparatively still very expensive compared to standard PC 100 and PC 133 SDRAM, and PC 1600, PC 2100, PC 2700, and PC 3200 DDR RAM. But motherboards with the required chipsets soon became available that allow Pentium 4 processors to use DDR RAM - and the latest development called dual-channel DDR RAM.

The table below shows the history of RAM from 1987 to 2002. The PC66 to PC133 in the three lighter blue rows refers to SDRAM.

Rambus RAM is shown in the two yellow rows, and DDR RAM is shown in the three dark blue rows. Rambus memory was used exclusively by the early motherboards that run the early Intel Pentium 4 processors, but has now been replaced by DDR and DDR2 RAM for both Intel and AMD processors, probably because it is a much more expensive alternative.

You can visit its manufacturer's site for more information about it. -

Rambus - http://www.rambus.com/

FPM and EDO RAM is no longer used in motherboards, but it was used for nearly a decade, and was usually supplied in the form of SIMM modules (Single In-Line Memory Modules). Towards the end of its life, EDO RAM could be purchased in the same DIMM module (Dual In-Line memory Module) form as DDR RAM.

FSB (the Front Side Bus) and DDR RAM

Ordinary SDRAM (the forerunner of DDR RAM) comes in types that run at official speeds of 66, 100, and 133MHz, i.e., usually at the same speed as the maximum official Front Side Bus (FSB) speed of the motherboards it runs on. It has been superseded by DDR and DDR2 RAM.

Setting unofficial FSB speeds is called overclocking the processor and the RAM.

The FSB is the network of interconnections between the various parts of the motherboard, so the FSB speed is the speed/frequency that the motherboard allows the FSB to run at.

On older motherboards the FSB speed is set by jumpers on the motherboard itself, but on most recent motherboards it is set in the BIOS setup program. The higher the number of FSB settings (exceeding the official FSB) that the jumper settings or BIOS provides, the more overclockable the motherboard is.

DDR SDRAM uses a new technique to transfer data that effectively doubles its speed. This kind of RAM used to be used only on motherboards that run AMD Socket A Athlon and Duron processors.

Intel Pentium 4 processors used to use only Rambus RDRAM, but now RDRAM has been eclipsed by DDR and dual-channel DDR RAM for both Intel and AMD processors.

Dual-channel DDR RAM is a misleading name for recent development that allows the motherboard to run ordinary DDR RAM at an effective speed of double its maximum running speed per module. Two ordinary DDR memory modules have to be fitted so that they can be accessed together. As usual, only motherboard's with specialised chipsets can make, say, DDR400 RAM run at an effective speed of 800MHz, or DDR333 run at an effective speed of 666MHz. Motherboards that support both the single-channel and the dual-channel modes of operation are available for both Intel Pentium 4 and AMD Athlon XP processors.

Remember that the AMD Athlon 64 processors have memory controllers built into them instead of having them on the motherboard, but the motherboard itself still have to support duel-channel mode. Its user manual provides the instructions of how the modules have to be installed to operate in dual-channel mode.

Most of the comments I've found on the web about the benefits of having DDR RAM running in dual-channel mode say that it does not increase the performance of a system much over the performance obtained when using single-channel mode.

PC 100 DDR RAM was named PC 1600 DDR RAM because of its data bandwidth (transfer capacity) of 1.6GB per second. A motherboard must specifically support it. Another term used for it is DDR200 because it runs at effectively twice the speed of the 100MHz FSB that it should run on.

Running DDR200 RAM on a 133MHz FSB would be overclocking it to run at an effective speed/frequency of 266MHz, which may or may not work, because some makes of RAM modules can be overclocked and others refuse to work if overclocked. In any case, you should not overclock any of the devices (processor, video card, RAM) in a computer by increasing the FSB speed unless you have researched the possibilities of doing so first on the Internet.

PC 2100 DDR RAM is just the DDR version of ordinary PC 133 SDRAM. It was named PC 2100 because it has a data bandwidth of 2.1GB per second. Motherboards that support it use an FSB set at 133MHz, which then produces an effective 266MHz bus speed between the processor and the RAM memory.

PC 2700 and PC 3200 DDR RAM is also known as DDR333 and DDR400 respectively.

See the table below for a list of DDR RAM that shows the names for it, the system FSB speeds that it runs on, and its effective maximum running speed/frequency.

The PC Name is derived from the RAM's bandwidth, which is the amount of data in megabytes per second (MB/s) that it can transfer per clock cycle.

For example, data is transferred in blocks of eight bytes. DDR400 RAM has an effective clock speed/frequency of 400 million clock cycles per second (400MHz), so if only one byte of data is being transferred per clock cycle, the bandwidth is 400 MB/s, but since blocks of eight bytes of data are transferred per clock cycle, the bandwidth is 400X8, which is 3200MB/s. Hence its PC Name of PC3200.

Another way to derive an idea of the speed of RAM is to use the module's cycle time, which is the amount of time needed to complete one clock cycle. A cycle time of ten nanoseconds (10ns) means that 100 million cycles are possible per second, because the chips run at up to 100MHz, which is another way of saying that the frequency is 100 million cycles per second. To reach 133MHz, you need an access time of 7.5ns; for 166MHz, 6.0ns, etc. - See the table below. 1ns = a billionth of a second, or 10 to the power of minus 9, where a billion = 1,000 million, so a billion divided by the 10ns cycle time for PC100 SDRAM comes to 100 million cycles per second.

However, there are many other factors that affect or determine how fast RAM is. For example, the famous CAS latency, or CL.

If your computer has low-latency memory modules, to make sure that they have been detected correctly, enter the BIOS setup program. The RAM settings are usually on a page in the BIOS called something like Chipset Features Setup. If there is an option called SPD (Serial Presence Detect), enabling it makes the BIOS set the optimal timings. SPD refers to a small chip on each memory module that holds the latency settings information. Note that the BIOS doesn't always read the information properly. If you suspect that to be the case, you can set each of the values manually in the BIOS. The lowest settings are the fastest.

Using the fastest RAM modules is only necessary if the computer works as hard as it does while, say, encoding video. For less intensive general-purpose computing applications, slower RAM is good enough.

Computers used mainly for playing the latest graphics-intensive games as well as possible use the latest ATI Radeon and nVidia GeForce video/graphics cards, which have a graphics processing unit (GPU) and currently have 256MB of DDR RAM onboard, so the speed of the system RAM is not of much importance.

DDR2 SDRAM and the motherboards that support it

JEDEC is the body responsible for standardising RAM, and it has had the specifications for DDR2 RAM approved since September 12, 2003.

Motherboards that support DDR2 RAM and Intel processors have been available for some time.

DDR3 RAM and the motherboards that support it have recently become available.

DDR3 vs. DDR2 - http://www.anandtech.com/memory/showdoc.aspx?i=2989

The next item on this page deals with DDR3 memory.

May 24, 2006. - AMD has made its entire range of Athlon 64 X2 dual-core 64-bit processors available as Socket AM2 versions, and has added the AMD Athlon 64 X2 4000+ and 5000+ dual-core processors to the range.

According to AMD, the time has arrived to move its entire processor range, including the entry-level Sempron processors to DDR2 memory.

February 21, 2006. - "The adoption of DDR2 memory for Intel-powered systems turned out to be much slower than expected, and the breakthrough was not until the introduction of DDR2 support for the mobile platform. While this did not actually hurt Intel, such a slow technology adoption last year could have stopped the recent tailwind that has put AMD into its current favorable position. The situation is different now. While there is still little performance benefit in using DDR2, memory configurations of over 1 GB are going to be cheaper soon with DDR2. It won't be long until regular 1 GB DDR2 DIMMs-non-enthusiast products-will hit the price points that are currently occupied by basic DDR400. Finally, 2 and 4 GB RAM configurations will become fairly affordable. Introducing a new platform while waiting for the memory to become reasonably priced is pretty much like the story of the chicken and the egg: which comes first? Fortunately, since both AMD and Intel are making the switch to DDR2-800 at the same time, we expect this transition to be both quick and beneficial to everyone." -

A Look At AMD's Socket AM2 Platform -

"Although the DDR2-powered Athlon 64 platform is now up and running, AMD will not release it until June 6th [2006]. While this is mainly a business decision, it also has the benefit of leaving some time for performance optimizations..."

http://www.tomshardware.co.uk/...review-1600.html

Below is a table showing the bandwidth of DDR-266 (PC2100) to DDR-400 (PC2700) and DDR2-400 to DDR2-800, plus the FSB speeds of the motherboards that support it.

Note the correlation between the PC Name and the single-channel mode's bandwidth in megabytes per second - MB/s. The dual-channel mode's bandwidth is double the single-channel mode's bandwidth.

The PC Name of a module of DDR RAM is derived from its bandwidth in MB/s.

It's easy to derive the PC Name from the DDR Type. Data is transferred in blocks consisting of eight bytes each, therefore multiplying the effective speed of the RAM by eight gives its bandwidth.

For example, DDR333 has an effective speed of 333MHz, which is the equivalent of 333 million cycles per second. The bandwidth is the amount of data that can be transferred per second. This RAM transfers eight bytes of data per clock cycle, so multiplying it by eight gives it a bandwidth of 2664 megabytes per second (MB/s).

In other words, the bandwidth is 2664 MB/s because an effective frequency of 333MHz would have a bandwidth of 333MB/s if only one byte of data was transferred per clock cycle, but eight bytes of data are transferred clock cycle, so the real bandwidth is 2664MB/s.

This is rounded up to 2700 to give it the PC Name of PC2700. In the same way, DDR400 becomes 400X8 = 3200, which becomes PC3200.

BIOS settings for DDR2 RAM

The BIOS setup program for a particular motherboard provides settings for the memory that can be modified/overclocked or enabled/disabled.

The user manual that comes with a brand-name PC or motherboard should have a BIOS section that provides information on the settings that are available. If you don't have such a manual, you should be able to download a copy in the PDF format from the PC or motherboard manufacturer's site for a particular make/model of PC/motherboard.

For example, the Asus P5WD2-E Premium Edition motherboard has a chipset that is supposed to support a maximum of DDR2-667 memory, but its BIOS has the settings that allow DDR2-800 and DDR2-1066 memory to be used.

The FSB setting can often be changed in the BIOS. When it is set at 200MHz in the BIOS of the above-mentioned motherboard, the settings in the image shown below become available (DDR2-400MHz to DDR2-800MHz).

However, when the FSB is set to 266MHz, the settings in the image below become available (DDR2-400MHz to DDR2-1067MHz).

Note that the BIOS settings are not standardised for all motherboards. It is up to the motherboard manufacturers which settings they choose to make available for a particular model of motherboard. For example, if a motherboard manufacturer wants to restrict the ability to overclock the processor and memory, the BIOS settings that allow the overclocking of those components will not be made available. This is a good idea from a support point of view, because people with no knowledge about overclocking often jump in at the deep end and ruin components, which are then sent back to vendors as being dead on arrival.

I'll be adding more information about DDR2 RAM as I come across it.

DDR3 SDRAM and the motherboards that support it

Motherboards and the new DDR3 RAM memory that they support are now available.

June 5, 2007 - Pipe Dreams: Six P35-DDR3 Motherboards Compared -

"Intel's P35 Express chipset represents next-generation processor and memory compatibility. While other media outlets consider the 'DDR2 v DDR3' debate, we instead analyze six motherboards that support the newest memory 'standard'..." -

http://www.tomshardware.co.uk/...review-2321.html

DDR3 memory components are twice as fast as the highest speed DDR2 memory components. The table below shows both the DDR3 and PC names for different module speeds (e.g., DDR3-800/PC3-6400), and their main specifications.

ARTICLES ON DDR3 MEMORY

DDR3 SDRAM - http://en.wikipedia.org/wiki/DDR3_SDRAM

DDR3 vs. DDR2 - http://www.anandtech.com/memory/showdoc.aspx?i=2989

What is DDR3 Memory? -

http://www.simmtester.com/page/news/showpubnews.asp?num=145

ECC stands for Error Correcting Code.

It is error correction hard-coded into the RAM chips themselves. ECC RAM - also known as parity RAM - is more expensive than other types, and is mainly used in mission-critical systems such as network servers that work around the clock.

Registered or buffered RAM has a built-in buffer that stores the data before it is transferred to the hardware memory controller. It increases the reliability of the RAM enormously. Even so, most of the RAM used in personal computers is unbuffered, and works reliably enough in that role.

DDR RAM modules that are both registered and have ECC are available, and modules that are registered without ECC, or are unbuffered (not registered) but have ECC are also available.

You can only install registered and/or ECC RAM in a system if it is supported by the motherboard. For current systems, this will be DDR RAM that is registered and/or incorporates ECC.

So, ECC detects and corrects memory errors, and registered means that the RAM registers memory information for one clock cycle to ensure that all communications with the memory controller (part of the motherboard's chipset, or built into the processor, as with the AMD Socket 939 Athlon 64 processors) can be more effectively checked and controlled.

Registered and ECC memory technology is designed to provide the greatest possible stability and reliability. Unfortunately, it slows down the RAM's data bandwidth. Moreover, because it requires a more involved manufacturing process, it is more expensive than non-ECC and unregistered RAM. Speed and price are the main reasons why you're unlikely to find this type of memory in the average home computer, but it is often found in high-end mission-critical workstations and servers.

Can you mix and match ECC and non-parity modules?

No! When adding additional memory, you need to match the RAM that is already in the system. To determine if the system has parity (ECC) RAM simply count the number of black memory chips on each module. Parity and ECC memory modules have a chip-count divisible by three or five. Any chip-count not divisible by three or five indicates that it is non-parity RAM module.

Still confused about the different types of RAM?

It is very easy to become confused with the different types of RAM that will or will not run on the different types of motherboards that support Intel or AMD processors.

Start by remembering that motherboards that support Intel processors never support AMD processors, and you are half way towards clearing up the confusion.

The motherboard must support a given processor if you are to use it. It is then just a simple matter of consulting the motherboard's manual to find out the types of RAM and the processors that it supports.

If you don't want to do that and you know the make and model of your brand-name computer, or the make and model of the computer's motherboard, you can find out which RAM it supports by using the UK or US Crucial Memory Selector provided at the top of this page.

Otherwise, if you don't already possess a manual for your computer's motherboard, you can download a copy from its manufacturer's website. As long as you only install items on a motherboard that are certified by its manual to run on or with it, you can't go very far wrong.

Most systems that have motherboards that use superseded SIMM memory modules require you to use matching pairs of modules to fill a bank of slots on your motherboard. If you fail to match them correctly, the system won't even boot.

For example, if you want to install 64MB of EDO RAM that comes in the outdated SIMM module form, you may have to install two matching 32MB modules instead of going with just one 64MB module, or one 32MB module plus two 16MB modules. Therefore, always check your system and motherboard manuals before you place an order.

Note that only dual-channel DDR RAM modules have to be installed in pairs. You do not need to install DIMM (SDRAM or DDR RAM) modules in pairs. Modern motherboards are also often much more forgiving about which DIMM modules can be fitted - they do not all have to be of the same capacity. - A 64MB module can be installed with 128MB and 256MB modules.

Remember, never skimp on quality when it comes to RAM.

Even when buying a new PC always obtain a system specification and check which make of RAM is installed.

Only grade-A memory will do, and it is only manufactured by the major manufacturers of RAM.

RAM is probably the most critical system component. Every bit of data passes through it to get to the processor, so it has to be 100% functional 100% of the time if data corruption is not to take place.

It is a fact that many program crashes can be attributed to cheap, error-prone or defective RAM. Therefore, if the system has generic, low-cost RAM, insist that grade A RAM from one of the major manufacturers is installed.

The major manufacturers of RAM are Crucial Technology (also known as Micron Technology), Rambus, PNY (uses Siemens chips), Kingston, Corsair, LG, Hyundai, Mushkin, and Samsung.

If the vendor's advertisement, or system specification doesn't name the manufacturer, then it is usually generic RAM that is on offer, much of which is not likely to be grade A RAM.

If the manufacturer of the RAM isn't one of those named above, to find out information and read reviews on it, you can enter its name in the Google search box provided at the top of this page.

Google searches

To conduct your own search of the web for information on RAM, or flash memory, or specific products mentioned on this page, you can make use the Google search box at the top of this page (with its Web radio button enabled).

PC Buyer Beware! Copyright © Eric Legge 2004-2008. All rights reserved.