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RAM Memory - How to Choose the Right Kind of Memory for Your Desktop or Laptop PC - Page 1


This section of this website consists of two long pages providing information on the different types of RAM memory used in desktop and laptop PCs since 1997 when SDRAM was first made available to the present reign of DDR3 SDRAM memory. Information on USB flash (thumb) drives and memory cards is provided on Page 2 of this article after the information on RAM memory ends.

SDRAM memory evolved into DDR SDRAM memory - now up to DDR3. RAM memory, which cannot retain its data, has not been replaced by flash memory, which, as in a USB flash drive, can retain its data, because flash memory only has a limited number of write cycles that will be reached relatively far more quickly if it were used as main memory compared to how quickly it would be used in an SSD drive that also uses flash memory. That is not the case with DDR memory, because it has an unlimited number of read and write cycles. The older the computer the more difficult it is to buy the correct memory for it, not because it isn't available, but due to the sheer profusion of different types and capacities and the support or lack of it provided by the motherboards in which it is installed. Having read the information provided here, you should have a good idea of how matters stand in the world of memory. A wide range of problems are dealt with separately in the RAM Memory Problems section of this website.

RAM MEMORY PROBLEMS AND SOLUTIONS

Click here! to visit the page on this site devoted to RAM memory problems and their solutions.

Two DDR3 RAM memory modules  with heatspreaders attached installed in  a desktop PC's motherboard's yellow and green DIMM slots

If you are just seeking information on how to install RAM memory, click here! to go to Page 2 of this article. If you are seeking information on RAM memory itself, read on...

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.

That said, computers can make use of technology called DMA (Direct Memory Access) to bypass the processor: "Direct memory access (DMA) is a feature of modern computers and microprocessors that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards and sound cards."

Unlike most other hardware components, RAM memory does not require a software device driver to be installed in order to function. All you have to do is install it and Windows, or any other operating system, can use it if it is compatible with the motherboard that it is installed in.

In 2012, most laptop and desktop PCs come with 4GB of memory, which can be increased by installing extra memory that complies with the motherboard's possible configurations, and most now have a 64-bit version of Windows 7 (Windows 8 is expected to be released in the final quarter if 2012 and its memory requirments are the same as that of Windows 7).

The image above shows two DDR2 RAM memory modules, made by Corsair, with heat spreaders fitted, installed in two of four DIMM memory slots of a desktop PC motherboard.

A memory module used in desktop PC motherboards is called a DIMM module. SODIMM modules are used in laptop PCs. The image below shows a close-up of a 4GB SODIMM module.

4GB SODIMM laptop RAM memory module

This is the part number on the Hynix laptop SODIMM module - HMT351S6BFR8C-H9.

Entering it in a search engine finds plenty of suppliers. I saw some available on eBay. Just remember that you need a 64-bit version of Windows Vista / 7 / 8.1 in order to be able to use more than 4GB. A 32-bit version of Windows cannot use more than 4GB (3.2GB to be precise). If you don't know which version you have, enter the following search query into a search engine: 32 bit or 64 bit windows - adding your version of Windows.

You only need matching modules if you want to run the memory in dual-channel mode (more detailed informatiion on that mode is provided in the article), which is slightly faster. If you visit crucial.com and search for your model of PC, PC motherboard or laptop, using the Memory Advisor will tell you which capacities of memory modules it can use.

Read this:

Matching Modules for Dual-Channel -

http://www.tomshardware.co.uk/answers/id-1730703/matching-modules-dual-channel.html

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 desktop and laptop computers is expressed in megabytes (MB) and gigabytes(GB). A gigabyte (1GB) is 1024MB. Most desktop and laptop computers that came with Windows XP preinstalled came with 512MB. However, this increased to gigabytes when Windows Vista was released in January 2007. RAM modules can still be purchased with MB capacities, but the vast majority of new desktop and laptop computers have modules with GB capacities.

A computer with Windows Vista preinstalled should have a minimum of 2GB or RAM memory to run comfortably, however, 1GB of RAM memory in computers running a 32-bit version of Windows 7 should suffice, because the 32-bit versions of Windows 7 can run on a comparatively low-spec netbook computer, most of which currently only have 1GB of memory (January 2010).

Windows 8 was made available on 26 October 2012. The memory requirements of Win8 are the same as those of Windows 7 and Windows 8 runs faster on most computers than Windows 7 on the same amount of memory.

I myself have a laptop and a desktop PC that run Windows 7 on 1GB of RAM memory very comfortably doing regular activities such as playing DVDs, running office software and accessing the web, which is what most people use a computer for. Both computers used to have Windows Vista installed, which did not run as comfortably on the same amount of memory.

32-bit versions of Windows cannot use (memory-address) more than 3.5 or less of memory; 64-bit versions of Windows can support far more memory than most home users will require for many years to come. The Windows 7 Professional, Enterprise and Ultimate versions can address (provide addresses to each bit so that be turned on or off to represent a 1 or a 0) up to 192GB of memory, the Home Premium version, used by most home users, supports 16GB. The Windows 7 Home Basic version, which is designed for emerging markets and is not available in the first-world countries, is limited to 8GB, because the computers used in those parts of the world are not required to use more than 1GB to 4GB. It comes in 32-bit and 64-bit versions, but, as is the case with Windows XP, is limited to using the Internet Explorer 8 web browser.

However, up to 4GB of memory, the 64-bit versions require twice as much memory as the 32-bit versions, so the minimum a 64-bit version should have is 2GB for Windows 7 and 4GB for Windows Vista. Most computers in use currently use a 32-bit version of Windows.

The following webpage tell you how to find out which bit-version of Windows 7 is installed (the information also applies to Windows Vista).

32-bit and 64-bit Windows: frequently asked questions -

http://windows.microsoft.com/en-US/windows7/...

Note also that even with a 64-bit processor and a 64-bit version of Windows XP/Vista/Windows 7, the motherboard's chipset must support at least 8GB of address space and the system's BIOS setup program must support memory remapping. Read this Q&A on this website for more information on those requirements: My computer running the 64-bit version Windows 7 Home Premium isn't using all its 4GB RAM memory.

To find out which bit-version of Windows you have, in Windows XP go Start => Control Panel and look for System and look on the General tab of the System Properties window. In Windows Vista choose the Classic View in the Control Panel. In Windows 7, just enter the word system in the Start => Search programs and files box to be provided with a clickable link to the System Properties window.

Note that the bit information might not appear on systems that have been customised by their manufacturer. It is safe to say, in my opinion, that if the bit information is not provided then your version is 32-bit. The 64-bit versions I have seen make it clear that they are on the General tab of the System Properties window. The 64-bit version requires 64-bit device drivers for hardware such as printers, graphics cards, mice, keyboards, etc. Therefore, if you attempt to install a 32-bit driver, you will be told that you require a 64-bit driver. 64-bit drivers cannot be used on a 32-bit version of Windows.

If you need to find out that information, enter a search query such as: how to find out if windows [xp, vista, windows 7 and 8] is 32-bit or 64-bit in a search engine.

For example, in Window 7, enter msinfo32 in the Start => Search... box to bring up a link to the System Information window. Look under System Summary => System Type. An X86-based PC is running a 32-bit version of Windows; an X64-based PC is running a 64-bit version of Windows. The msinfo32 command that brings up System Information works from Windows XP to Windows 8. It is entered in the Run box in XP.

Here are the facts and recommendations about memory for different types of users, versions of Windows, design-software applications and PC games supplied by Crucial.com:

Computer memory requirements: How much memory do you need? -

http://www.crucial.com/support/howmuch.aspx

Note well that the new AMD and Intel processors that have integrated graphics chips use the system's RAM memory, reducing the amount available to the system, so, if performance is an issue, such as when playing the latest games, the performance of the system memory has to be taken into consideration. This means having enough memory in the first place and using the fastest memory you can afford.

Motherboard and memory manufacturers say that 8GB of memory is ideal to run AMD's Llano processors (APUs), which all have onboard graphics chips. A 64-bit operating system is required to use more than 3.12GB of memory, which for most users means having a laptop or desktop PC running the 64-bit versions of Windows 7 - the Home Premium, Professional and Ultimate versions. The following article reviews seven 8GB memory kits:

http://www.tomshardware.co.uk/llano-apu-memory-performance,review-32268.html

MemInfo from http://www.carthagosoft.net/MemInfo.php is a very useful tool that monitors the amount of memory being used or free and the amount of virtual memory being used by Windows (its Page File on the hard disk) to swap data in and out of real RAM memory.

If, for example, you notice that much more memory is being used all of a sudden, putting the amount of memory in use in the red, this can be caused by a badly written virus that is making Windows use much more memory than is usual. When you see something like that happening, it needs to be investigated by a full system malware scan.


RAM memory that is not recognized or only half or a quarter of it is recognized

Computer users 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 are advised to try using the Crucial Memory Advisor on crucial.com (US) or crucial.com/uk (UK) in order to make sure that you don't purchase RAM that isn't supported by your brand-name desktop or laptop computer or the computer's motherboard. Indeed, if you're contemplating buying a new motherboard for a desktop PC, it would be a good idea to find out if it is listed by Crucial before you buy it.


Mixing brands of RAM can often cause problems

Using cheap no-brand, generic RAM can be a common a source of system failure, so make sure that you purchase RAM manufactured by one of the major manufacturers such as Crucial, PNY, Kingston, Samsung, Panasonic, Corsair, OCZ, Transcend, etc. (Note that many of these memory manufacturers use memory chips made by Samsung.)

Cheap, no-brand RAM can be especially prone to failure if the processor has been overclocked to a faster speed than its designated speed by increasing the frequency (speed) of the system bus. The cheap RAM will probably not be able to handle the increase and cause Fatal Exception and Page Fault failures.

Because of the problems that can occur, it's never a good idea to mix modules of the same specification made by different manufacturers, or to use brand-name modules with generic, unbranded modules of the same specification. Using modules that have different specifications should also be avoided, because, if the system works, all of the RAM will run at the speed of the slowest module.

That said, if you have a PC that has memory made by a manufacturer of quality products, adding memory made by another manufacturer of quality products will be less problematic than if either or both manufacturers don't have a reputation for quality products. For example, I have a laptop that came with 2GB of memory made by Transcend. I bought another 2GB from Crucial, using its Memory Advisor, which provided memory of exactly the same specifications as the Transcend memory. Crucial could do that because it knew what memory was installed on the make/model of laptop and simply matched it. The two makes of memory work perfectly together.

The motherboard's website or newsgroup may contain information or postings about troublesome brands or particular peculiarities.

Windows 7 is the latest version of Windows. Home users were able to buy the version of their choice on 22 October 2009. Most netbook computers are presently running Windows XP because Windows Vista runs very slowly on their relatively low specifications of memory and processor, but Windows 7 runs well on them because of its lower hardware requirements. To such a extent that Microsoft will not be creating a netbook version of Windows Vista.

There have been many different types of RAM memory in use since it first was used in computers. The RAM memory used in current PCs comes in the form of DDR and DDR2 and DDR3 memory modules. The correct type that the computer's motherboard supports has to be used. Some motherboards can support two types, such as DDR and DRR2, but most motherboards only support one type. A kit consisting of two 1GB modules of DDR2 memory, for use in a desktop PC, made by Crucial, is shown below. The upper side with the notch and the metallic edge is keyed to fit into the appropriate memory (DIMM) slot, therefore it cannot be installed in the wrong type of slot unless the installer uses the kind of force that will probably destroy the module.

A memory kit consisting of two 1GB  DDR2 memory modules (DIMMs) made by Crucial

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.

Some high-speed RAM memory modules come with passive heatsinks fitted to them that keep them cool. These heatsinks can also be purchased and replaced. Names for memory-cooling devices are heatspreaders, heat spreaders, ramsinks, memory cooling kits, RAM heat sinks, etc. You can find vendors for them by entering one or more of those names as search queries in a search engine. Cooling units are also available for high-performance memory. For example, Crucial.com sells a Ballistix Active Cooling Fan unit for its Ballsitix high-performance memory that fits over the DIMM modules to provide extra cooling that gets rid of dead spots in the flow of air around them.

The image below is of a Corsair memory module with a passive heatsink fitted to it.

Corsair RAM memory module with a built-in passive heatsink

How To Replace Memory Heat Spreaders -

http://www.tweaktown.com/guides/1491/...

Most of the current 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 latest Intel Socket LGA1366 quad-core Core i7 processors (CPUs) can only run on DDR3 memory (Socket LGA1366 motherboards require DDR3 memory and Core i7 processors can only run on Socket LGA1366 motherboards).

The latest AMD Phenom II quad-core and triple-core processors can use DDR3 memory when installed in a Socket AM3 motherboard and DDR2 memory when installed in a Socket AM2+ motherboard. (They can be used with both Socket AM2+ and Socket AM3 motherboards.)

The modules are installed in the DIMM memory slots on the PC's motherboard. Most desktop-PC 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.

Note that most laptop PCs only have two memory slots, so you can add additional memory if one of the slots are free. If both slots have memory modules installed in them, to increase the amount of memory you will have to remove one or both modules and install modules with a higher capacity. How much memory a laptop supports and where it is installed is information provided in its user manual, which should be available as a download from its manufacturer's website if you don't have a copy.

MSI K8N Diamond Plus Socket 939 motherboard with two SLI PCI Express slots and four DIMM RAM memory slots

MSI K8N Diamond Plus Socket 939 desktop-PC 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.com.

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 motherboards support all three types. A DDR3-supporting motherboard will not support DDR memory, but it might, but not necessarily, support DDR2 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 or triple-channel mode with DDR3 installed in Socket LGA1366 motherboards that run Intel's Core i7 quad-core processors.

Note that Intel-based motherboards, like AMD-based motherboards, now only use dual-channel mode. Some Intel-based Socket LGA1366 motherboards and the onboard memory controllers of the Intel processors can use them use triple-channel mode, but they are so rare that memory reviews only review dual-channel (dual-module) memory kits. This was the situation in December 2010. Intel's Sandy Bridge second-generation Core i3, i5 and i7 processors are now available for both desktop and laptop PCs.

December 6, 2010. - Note that Intel's yet-to-be-released processors code-named Sandy Bridge that incorporate the graphics processor in the same die (processing unit) as the processor itself only incorporate a dual-channel DDR3 controller, which suggests that the triple-channel system used by the Socket LGA1366 platform is being abandoned.

Modern AMD-based motherboards (motherboards that run processors made by AMD) 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 can be accessed as if they were a single module and outperform a single 2GB module that can only operate in single-channel mode.

Now, with the arrival of DDR3 memory and Intel's Core i7 processors that run on Socket LGA1366 motherboards, for the first time, Intel has a range of processors with an inbuilt memory controller that can run memory in triple-channel mode (three memory modules that can be accessed at the same time as if a single module). When two memory modules are installed, the triple-channel architecture operates in dual-channel mode.

You can make use of the Crucial Memory Advisor, provided by crucial.com/uk (UK) and crucial.com (US), that provide RAM memory on a brand-name desktop or laptop PC or motherboard basis. By making use of the applicable advisor, as long as you identify your computer's make/model or its make/model of motherboard, you are guaranteed to obtain the correct memory for your computer or you get your money back.

Intel's Core i7 quad-core processors can use triple-channel mode

Until the Socket LGA1366 Intel Core i7 quad-core processors first became available in November 2008, only AMD's Athlon 64 (single-core and dual-core) and Phenom (quad-core) processors could use dual-channel mode, because it requires the memory controller to be built into the processor, and Intel's processors did not provide that feature. Dual-channel mode requires two memory modules to be used in tandem. If the motherboard has four DIMM memory slots, it can run two pairs in tandem in dual-channel mode. But now the Core i7 processors also have an built-in memory controller. Core i7 is Intel's first platform to use only DDR3 RAM memory. Moreover, it uses a built-in triple-channel memory controller, so DDR3 DIMM modules will soon be available in packs of three to make use of the six DIMM memory slots that Socket LGA1366 motherboards have in order to use triple-channel mode. The first Socket LGA1366 motherboards, such as the MSI MS-7522 motherboard, that run the Core i7 processors, provide six memory slots. The motherboard's user manual shows which slot can be used for a single memory module, and which slots can be used for dual-channel and triple-channel mode. If all six slots are filled with identical modules, you will have two sets of modules running in triple-channel mode. As with dual-channel mode, triple-channel mode provides a small gain in performance.

Note that triple-channel mode was only supported by the first-generation Core i7 processors. To be specific the Intel Core i7-9xx Bloomfield, Gulftown Intel Core i7-9x0X Gulftown. Several Xeon processors, not used in home computers, also support it. Intel adopted dual-channel mode for all of its Core processors thereafter.

Multi-channel memory architecture -

http://en.wikipedia.org/wiki/Multi-channel_memory_architecture

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, which at that time was a huge amount of memory, but which Windows XP could not run on.

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 (which is only available as a 32-bit version) and Professional Editions (which has both 32-bit and 64-bit versions) should have no more than 3.5GB of memory installed, because they don't support more than that amount of memory. The maximum amount of memory that a 32-bit version of Windows can use is actually 3.12GB.) The 64-bit version of Windows XP Professional (Windows XP Professional x64 Edition) supports up to 128 gigabytes (GB) of RAM and 16 terabytes of virtual (swap-file) memory on the computer's hard disk drive.

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. A 32-bit version of Windows XP/Vista cannot use more than 3.12GB of memory, but you can install 4GB. Any more than that will slow the computer down.

See the table further down this page for the memory requirements of Windows 7.

If you want to install more than 4GB of RAM memory and have Windows support it, the computer must have a 64-bit processor, which almost all new computers now have, and be running a 64-bit version of Windows that supports more than 4GB. To be a 64-bit system, a 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.

Compare the versions of Windows Vista -

http://windows.microsoft.com/en-us/windows-vista/products/compare

The 32-bit versions of Windows XP and Windows Vista support up to 4GB of RAM, but can only use 3.12GB in practice. However, most of the 64-bit versions of Windows Vista support a huge 128GB of RAM, which cannot be installed on current motherboards because only 8GB DIMM modules are currently available, with 16GB modules on the way, and even motherboards that support Intel Core i7 quad-core processors only have six DIMM memory slots.

Memory maximums for the different versions of Windows:

Windows XP Home 32-bit: 4GB - Windows XP Professional 32-bit: 4GB - Windows XP Professional 64-bit: 128GB - Windows Vista Home Basic 32-bit: 4GB - Windows Vista Home Basic 64-bit: 8GB - Windows Vista Home Premium 32-bit: 4GB - Windows Vista Home Premium 64-bit: 16GB - Windows Vista Ultimate 32-bit: 4GB - Windows Vista Ultimate 64-bit: 128GB+ - Windows Vista 32-bit: 4GB - Windows Vista 64-bit: 128GB+

This page provides the details for all of the current versions of Windows, including Windows 7:

Memory Limits for Windows Releases -

http://msdn.microsoft.com/en-us/library/aa366778(VS.85).aspx

Memory Limits: Windows 7:

Version
Limit in 32-bit Windows
Limit in 64-bit Windows
Windows 7 Starter
2.0GB
2.0GB
Windows 7 Home Basic
4.0GB
8.0GB
Windows 7 Home Premium
4.0GB
16.0GB
Windows 7 Professional
4.0GB
192.0GB
Windows 7 Enterprise
4.0GB
192.0GB
Windows 7 Ultimate
4.0GB
192.0GB

This article explains how the current versions of Windows use memory and how you can increase the memory limits:

Access more memory, even on a 32-bit system -

http://windowssecrets.com/2008/12/18/03...

You can find out if a particular Intel or AMD processor is 32-bit or 64-bit from the following page:

Desktop CPU Comparison Guide -

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

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.

Why doesn't my Windows PC recognize the whole 4GB of memory I installed? -

http://www.crucial.com/support/recognize_memory.aspx

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

Pushing the Limits of Windows: Physical Memory -

http://blogs.technet.com/b/markrussinovich/archive/2008/07/21/3092070.aspx

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?

Note that the way in which Windows Vista uses virtual memory, which simulates RAM memory by using storage space on a PC's hard disk 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

After Windows Vista was released, most of the current desktop PCs and laptop/notebook computers that were being sold new with Windows XP came with 1GB of RAM memory in anticipation of being upgraded to Windows Vista Home Premium or Windows Vista Ultimate.

Fortunately, upgrading a deskop or laptop computer's RAM is a relatively easy matter provided that the computer has one or more spare DIMM/SO-DIMM memory slots on its motherboard and you obtain the correct kind of DIMM module(s) for a desktop PC and SO-DIMM module(s) for a laptop PC.

If a desktop computer's motherboard only has two DIMM memory slots that each have a 512MB module installed in it, making a total of 1024MB (1GB) of memory, you can still upgrade the system to 2GB of memory if the motherboard supports 1GB modules in each slot (1024 x 2 = 2048MB = 2GB of memory). You could then sell the two 512MB 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.

Note that Intel's Socket LGA1366 Core i7 quad-core processors now have a memory controller onboard for the first time that can run DDR3 memory in triple-channel mode, so the motherboards that run them have six DIMM memory slots in order to run two sets of three modules in triple-channel mode. They can also run DDR3 memory in single-channel and dual-channel modes. AMD's processors have had an onboard memory controller for many years.

Note that Intel's yet-to-be-released processors code-named Sandy Bridge that incorporate the graphics processor in the same die (processing unit) as the processor itself only incorporate a dual-channel DDR3 controller, which suggests that the triple-channel system used by the Socket LGA1366 platform is being abandoned.

Intel's Core i7 quad-core processors can only use DDR3 memory. AMD's Phenom II quad-core and triple-core processors can be installed in both Socket AM2+ and Socket AM3 motherboards. They run on DDR3 memory when installed in a Socket AM3 motherboard and run on DDR2 memory when installed in a Socket AM2+ motherboard.

RAM memory modules: The warranty period

The warranty period for generic (unbranded) RAM memory modules is the usual twelve months. However, a brand-name manufacturer such as Crucial provides a lifetime warranty. That means that the memory is covered by the warranty as long as it is used by the purchaser in a computer that supports it. That amounts to about five years, because new types of RAM is always being released, and the older modules won't be supported by new motherboards.

See the Warranties page on this site for more information on them in regard to computers or their components. Individual components, such as the monitor, can have a longer warranty period than the computer itself.

Measures you should take before taking your computer in for repairs

Note that if you are sending a computer in for repairs, it's an excellent idea to make a note of the details (make, model, etc.) of all of the components, including the RAM, that is installed. It is a simple matter for a crooked technician to replace high quality components with cheaper ones.

You could put a small white dot of Tippex, or other non-removable mark, somewhere on the component so that you can check that it is still there when the system is returned. Taking close-up photographs of the system that have been verified by witnesses might provide proof of theft in a court case. However, the outfit responsible could accuse you of replacing the components yourself in order to receive compensation or better components in exchange for inferior ones, so you might not be able to obtain any redress. But at least you'll know never to deal with the place again. However, if you appeal to the chief executive there, and you look honest, you might have the matter put right.

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.

The following article uses a laptop PC to gauge the increase in performance with increased amounts of RAM memory and the performance gains made by using dual-channel mode instead of single-channel mode, but the findings apply to a desktop PC. The second article's title explains its contents.

How much RAM is enough? -

http://www.hardwareinsight.com/how-much-ram-is-enough/

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, Windows Vista and Windows 7 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.

For more information search for: system resources in windows 9x - which should cover what they are, why they are unrelated to the amount of RAM, how to manage them and prevent memory leaks, etc.


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 - or transferred directly to the hardware components that can use Direct memory Access (DMA), including disk-drive controllers, graphics cards, network cards and sound cards.

The RAM is conventionally controlled by the memory controller of the motherboard's chipset, or, as is now also the case with AMD Athlon 64 processors and Phenom processors and Intel Core i7 processors, by a memory controller built into the processor itself, which is capable of running the memory it supports in single-channel mode and in the faster dual-channel mode (plus triple-channel mode for the Intel Core i7 processors). More information on DDR, DDR2 and DDR3 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 mode (or triple-channel 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 or triple-channel mode is 5% to 10% faster than memory running in single-channel mode.

Identify the RAM memory in your system

If you want a quick way to identify a PC's processor, motherboard, and RAM, the free CPU-Z from cpuid.com is ideal. It provides plenty of information on those components in Windows 95/98/Me/XP/Vista and Windows 7. Download and install the program and look under its Memory and SPD tabs. CPU-Z identifies the make of the memory installed; Crucial's scanner does not. It is best to install a memory upgrade made by the same manufacturer as the existing memory.

Virtual memory (the Windows swap/paging file) is not RAM memory

Virtual memory is a reserved area of a hard disk drive used as a buffer or cache that serves the RAM memory. It is also known as a paging or swap file. If you want information on it in Windows XP's Help and Support, enter the words paging file in the Search box, because using the words virtual memory turns up nothing. The files used most frequently by running programs are stored in the RAM so that they can be accessed as quickly as possible. Files used less frequently by running programs are placed in the swap file. They're moved into RAM when required. Since accessing RAM memory is much faster than accessing the fastest of hard disk drives, the more the system has to use virtual memory, the slower it operates. All of the versions of Windows make use of virtual memory, but the more RAM the system has at its disposal, the less it needs to make use of virtual memory, and vice versa.

In Windows 95, 98, and Me the virtual memory settings are accessed by clicking on My Computer with the right mouse button, followed by clicking Properties in the menu that presents itself. Click on the Performance tab in the window that comes up, and then click the Virtual Memory button.

The procedure for Windows XP and Windows 2000 is the same for the first two steps, but then open the Advanced tab. The Performance Options window opens. Click on its Advanced tab. To change the settings, click on the Change button under Virtual memory.

Read Managing Processes and Tasks in Windows Vista to find out what the differences are between the Task Manager in Windows XP and Windows Vista.

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://m.techrepublic.com/article/windows-vista-superfetch-and-external-memory-devices/6039379

How To Move the Paging File in Windows XP - This article describes how to change the location of the paging file in Windows XP. The paging file is the area on the hard disk that Windows uses as if it were random access memory (RAM) This is sometimes known as "virtual memory." By default, Windows stores this file on the same partition as the Windows system files. You can increase the performance of Windows, and increase free space on the boot partition, by moving this file to a different partition. -

http://support.microsoft.com/?kbid=307886

Note that you shouldn't change the settings unless you know what you're doing. Windows 95/98/Me manages the virtual memory itself by default. Windows XP also manages the virtual memory itself by default, but it makes the size of the swap file 1.5 times the amount of available system RAM. If the system RAM is shared by a video chip on the motherboard, the amount of RAM available to the system (minus the RAM used by the video chip) is used in the calculation.

The system resources of Windows 95, 98, 98 SE, and Me

If a computer produces an error message that informs of a lack of system resources, this is not is not referring to a lack of RAM. System resources are a limiting factor in DOS-based Windows 95, 98, and Me. Two small 64KB blocks of the RAM used by DOS called Convention Memory are used to contain operating information about the programs and processes that are running. As this 128KB of reserved RAM memory comes close to being used up, those versions of Windows become unstable. To regain stability requires closing programs down or rebooting the computer. Because Windows 2000 and Windows XP don't make use this memory, the lack of system resources is not an issue with them.

System Resources FAQ - http://www.aumha.org/a/resource.htm

System Resource Issues -

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


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


EDO, SDRAM, DDR SDRAM and Rambus RAM

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 which is comparatively 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 allowed Pentium 4 processors to use DDR RAM - and the latest development of that time called dual-channel DDR RAM, which the processors made by AMD (but not those made by Intel) were able to employ, because AMD's processors had the required inbuilt memory controller instead of a memory controller on the motherboard. Intel's Core i7 quad-core processors are the company's first to use an inbuilt memory controller, which can run memory in dual-channel and triple-channel modes. Both of those modes were discussed further back in this article.

The table below shows the history of the types of RAM from 1987 to 2002. The PC66 to PC133 in the three lighter blue rows refers to SDRAM (Synchronous Single Data Rate) memory, the forerunner of DDR SDRAM.

Rambus RAM is shown in the two yellow rows, and DDR RAM is shown in the three dark blue rows. You can read about that type of memory here: http://en.wikipedia.org/wiki/Rambus.

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.

Table showing the history of RAM technology

FSB(the Front Side Bus) and DDR SDRAM

Ordinary SDRAM (the forerunner of DDR SDRAM) 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, DDR2 and DDR3 SDRAM .

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 all PC motherboards now set its frequency/speed 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.

Front Side Bus - http://en.wikipedia.org/wiki/Front-side_bus

DDR SDRAM (DDR, DDR2, DDR3 memory) uses a new technique to transfer data that effectively doubles its speed compared to SDRAM memory. You can read about the technology involved here: http://en.wikipedia.org/wiki/DDR_SDRAM. It achieves this by transferring data on the both the rising and falling cycles of the clock signal, instead of just transferring data once per clock signal, without increasing the clock speed/frequency.

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 in dual-channel mode. Even though dual-channel kits of two identical modules are on sale, special dual-channel modules are not used. Two ordinary DDR, DDR2 or DDR3 memory modules with the same specification and memory capacity have to be fitted so that they can be accessed together (with the triple-channel mode used by Intel's Core i7 quad-core processors, three identical memory modules have to be used).

Dual-channel architecture -

http://en.wikipedia.org/wiki/Dual-channel_architecture

Triple-channel architecture -

http://en.wikipedia.org/wiki/Triple-channel_architecture

Note that Intel's yet-to-be-released processors code-named Sandy Bridge that incorporate the graphics processor in the same die (processing unit) as the processor itself only incorporate a dual-channel DDR3 controller, which suggests that the triple-channel system used by the Socket LGA1366 platform is being abandoned.

As usual, only motherboard's with specialised chipsets can make, for example, DDR400 RAM runs at an effective speed of 800MHz, or DDR333 run at an effective speed of 666MHz.

However, the reports with regard to the performance increase of dual-channel configurations vary hugely. Some tests indicate that there are significant performance gains; others indicate next-to-no gain. Most of the comments I've found on the web about the benefits of having DDR and DDR2 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. The reports with regard to the performance of running DDR3 memory in triple-channel mode had yet to appear on the web at the time of writing (June 2009).

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 overclocking websites of which there are many. To find them, just enter overclocking as the search query in a search engine.

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.

The Motherboard's FSB Speed
PC Name
DDR Name
Double Data Rate (DDR) I/O Bus clock speed
100MHz
PC 1600 (8 X 200)
DDR200
200MHz (Twice the FSB)
133MHz
PC 2100 (8 X 266)
DDR266
266MHz (Twice the FSB)
166MHz
PC 2700 (8 X 333)
DDR333
333MHz (Twice the FSB)
200MHz
PC 3200 (8 X 400)
DDR400
400MHz (Twice the FSB)
266MHz
PC 4200 (8 X 533)
DDR533
533MHz (Twice the FSB)

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.

Cycle time
Maximum frequency
SDRAM bandwidth
DDR bandwidth
10.00ns
100MHz
800MB/s (PC100)
1,600 MB/s (DDR200)
7.50ns
133MHz
1064MB/s (PC133)
2,100 MB/s (DDR266)
6.00ns
166MHz
- -
2,700 MB/s (DDR333)
5.00ns
200MHz
- -
3,200 MB/s (DDR400)

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

The BIOS: Serial Presence Detect (SPD)

If your computer has low-latency memory modules, to make sure that they've 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 automatically. 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 presented 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 up to 2GB 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 and AMD processors have been available for some time.

DDR2 SDRAM - http://en.wikipedia.org/wiki/DDR2_SDRAM

DDR3 RAM and the AMD-based and Intel-based motherboards that support it have recently become available.

DDR3 vs. DDR2 - http://www.anandtech.com/show/2232

The next item on this page deals with DDR3 memory.

Below is a table showing the bandwidth of DDR2-400 to DDR2-1066, plus the FSB and effective FSB speeds of the motherboards that support it.

DDR Type
PC Name
Double Data Rate (DDR) I/O Bus clock
Single-Channel Mode DDR Bandwidth
Dual-Channel Mode DDR Bandwidth
DDR2-400
PC2-3200
100MHz
200MHz
3,200 MB/s
6,400 MB/s
DDR2-533
PC2-4300
133MHz
266MHz
4,266 MB/s
8,533 MB/s
DDR2-667
PC2-5300
166MHz
333MHz
5,333 MB/s
10,666 MB/s
DDR2-800
PC2-6400
200MHz
400MHz
6,400 MB/s
12,800 MB/s
DDR2-1066
PC2-8500
266MHz
533MHz
6,400 MB/s
12,800 MB/s

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).

BIOS DDR2 memory settings for a FSB of 200MHz

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

BIOS DDR2 memory settings for a FSB of 266MHz

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.


DDR3 SDRAM and the motherboards that support it

Motherboards that run the latest AMD and Intel quad-core processors 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 can transfer data twice as fast as the highest speed DDR2 memory components. The major advantage of DDR3 memory is the ability to transfer data at twice the rate of DDR2 memory. Moreover, the DDR3 standard allows for chip capacities of 512 megabits to 8 gigabits, allowing for a maximum memory module size of 16 gigabytes (16GB).The table below shows both the DDR3 and PC names for different module speeds (e.g., DDR3-800/PC3-6400), and their main specifications.

DDR3 Type
PC Name
Double Data Rate (DDR) I/O Bus clock
Effective data transfer speed
Bandwidth transfer rate
DDR3-800
PC3-6400
100MHz
400MHz
800MHz
6,400MB/s
DDR3-1066
PC3-8500
133MHz
533MHz
1066MHz
8,530MB/s
DDR3-1333
PC3-10667
166MHz
667MHz
1333MHz
10,660MB/s
DDR3-1600
PC3-12800
200MHz
800MHz
1600MHz
12,800MB/s
DDR3-1866
PC3-14900
233MHz
933MHz
1866MHz
14,930MB/s
DDR3-2000
PC3-16000
250MHz
1000MHz
2000MHz
16,000MB/s

ARTICLES ON DDR3 MEMORY

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

DDR3 vs. DDR2 - http://www.anandtech.com/show/2232

What is DDR3 Memory? -

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


Registered and ECC RAM

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 itself) 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 Crucial System Scanner Tool on crucial.com.

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 matching 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, etc.

With the triple-channel mode used by Intel Core i7 processors running on Socket 1366 motherboards, the modules have to be installed in matching sets of three to run in that mode. If matching pairs of modules (of the same type and capacity) are installed, the memory runs in dual-channel mode.

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, it might still be a respectable make, so to find out information and read reviews on it, you can enter its name as a search query in a search engine.


Web searches

To conduct your own search of the web for additional information on RAM or flash memory, or specific products mentioned on this page, you can enter a suitable search query into the web search engine of your choice.

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