RAM Memory: DDR, DDR2, DDR3, DDR4

The information you need to be able to choose the right type and capacities of RAM memory for a desktop or laptop PC

A pair of DDR3 Corsair RAM DIMMS with heatspreaders in their slots on a motherboard

A pair of DDR3 Corsair RAM DIMM modules with heatspreaders in their slots on a motherboard

This section of this website provides information on the different types of Random Access Memory – the RAM memory used in desktop and laptop PCs since 1997 when SDRAM was first made available to the present reign of DDR4 SDRAM memory. There were earlier types of memory, such as EDO RAM, but, as is the case with SDRAM, they are no longer being used. I only come across computers running DDR to DDR4 memory now.

The problems caused by faulty RAM memory

Since RAM memory is a crucial component, it must function 100% correctly all the time, otherwise it is responsible for a wide range of problems, some of the symptoms of which may appear to be caused by other components. The main problems are system crashes (sudden crashes, Blue Screens of Death (BSOD), etc) and freezes. Other symptoms are random restarts, file corruption that appears to be a software problem and the system issuing a BIOS beep code at startup.

If a relatively few memory addresses in the billions of such addresses go bad, which is usually the case, those bad addresses won’t cause problems until they are used – old old data is removed from addresses and new data is stored in them. RAM is an acronym that stands for Random Access Memory. The memory is used randomly by the system, so faulty addresses might not be used for a long time or might be used regularly, taking unused data out and put new data into them. Therefore, the fault can cause random system problems that are often unpredictable or irregular.

Memory diagnostic tools

1. – The Windows Memory Diagnostics Tool available in Windows 7 to Windows 10. Use this tool first. It works quickly, taking about half an hour to check 3GB of memory on a 32-bit version of Windows 7. The tool is under Administrative Tools in the Control Panel. It restarts the computer to run its tests and reports the result in the Notification Area when the system restarts. You need to be at the computer to read it because it comes up briefly and then disappears forever. The tool does not keep the report.

Bring up a link to it by entering the word memory in the Win7/10 Search box. If the computer cannot boot, use the Windows Repair media (disc for Win7 or flash drive for Win10) that can be created on any Windows 7/10 computer. The version in Win10 provides three levels of tests – Basic, Standard and Extended. The standard test is run by default, which detects most memory problems.

2. – Memtest86 is a free stand-alone, industry-standard tool that can be downloaded from https://www.memtest86.com/. It launches from a USB flash drive and provides a much more exhaustive set of diagnostic tests. It tests the memory independently of the operating system so it can be used on a computer running any version of Windows from Windows XP to Windows 10, or any other operating system.


Scroll down this single page or click the heading links to go directly to that information.

1. – Virtual memory and third-party memory managers
2. – RAM memory problems || How to install memory || How much memory do you need || SSDs & USB flash drives
4. – A fail-safe way to get the correct RAM memory
5. – Multi-channel memory architecture: Dual-channel DDR3 and quad-channel DDR4 memory
6. – Direct Memory Access – DMA
7. – RAM does not need a device driver
8. – Laptop SODIMM memory modules
9. – How much memory do the 32-bit and 64-bit versions of Windows Vista / 7 / 8.1 / 10 need
10. – RAM memory that is not recognized or only half or a quarter of it is recognised
11. – Low quality RAM and mixing brands can often cause problems
12. – Registered and ECC RAM memory
13. – UEFI/BIOS RAM memory settings taken from the BIOS section of motherboard’s user manual

POST: Strange RAM problem – memory not recognized by Windows 7 but identified in a Crucial scan

POST: Missing memory – Four good RAM modules, four good motherboard DIMM slots, only 8GB of 16GB shows in UEFI BIOS and Windows 10

POST: Under-used RAM: Windows 7 PC is only using 2.7GB of its 4GB RAM memory

POST: Memory limits – Why can my 64-bit Windows 10 PC only use 4GB of RAM memory?

POST: The causes of RAM memory problems and how to diagnose, troubleshoot and fix them

Virtual memory and third-party memory managers

Note well that regardless of whichever version of Windows a computer is running, its memory manager will manage the memory best. Windows also uses virtual memory – really disk space – when it runs out of real memory. You can set the virtual-memory swap file that Windows uses on the hard disk manually, but you should know what you are doing. An SSD should not make use of virtual memory at all – it should have been disabled automatically by Windows 7/8.1/10 when the computer runs from an SSD. It’s advisable to allow Windows to manage the real memory and the virtual memory. There are third-party memory managers that defragment the memory, but these are not necessary and can cause problems with the system that vary in their seriousness. They should not be used.

Memory management – https://en.wikipedia.org/wiki/Memory_management

The following video provides information on the virtual memory settings in Windows 10, but they are much the same in any version of Windows since Windows XP.

Windows 10 – Optimize Performance – Virtual Memory – Advanced System Settings – Speed Up Windows 10 –

RAM memory problems || How to install memory  || How much memory do you need || SSDs & USB flash drives

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, drawn from the main data-storage hard-disk and SSD drive(s), in the form of files for processing by a computer’s central processing unit (CPU), also known as the processor.

RAM memory problems

The RAM Memory Problems section of this website deals with them.

How to install RAM memory

For installation instructions, visit the How to install DDR/DDR2/DDR3/DDR4 RAM memory that is part of the Build Your Own PC section of this website.

If you have the user manual that came with a motherboard you bought or which can be downloaded from its manufacturer’s website, it provides all of the information about that particular model, such as how to install RAM memory, drives, processor, connect the motherboard to the power supply unit, etc. Some motherboards provide onboard diagnostic LED lights that indicate if a component is not working.

Asus Sabertooth X99 motherboard's button that indicates if the RAM memory is compatible

Asus Sabertooth X99 motherboard’s button that indicates if the RAM memory is compatible. Click the image to view its full size

Some motherboards provide a button on the board that when pressed indicates if the memory is compatible. The diagram below is taken from the user manual of the Asus Sabertooth X99 motherboard, showing its MemOK! button. Press the button after installing the memory. The LED lights up to indicate if the memory is compatible or not.How much memory do you need

Computer memory requirements: How much memory do you need?


SSD and flash drives use flash memory

(SATA) SSD drives, increasingly being used as alternatives or in conjunction with hard disk drives, and USB flash drives use expensive flash memory that retains its data when the device using it is switched off.

IDE PATA, SATA, SCSI/SAS Hard Disk (HDD), Solid State Drives (SSD) –


USB Flash Drives/Memory Sticks –


Annotated MSI 945GCM5 F motherboard showing its DDR2 memeor slots

Annotated MSI 945GCM5 F motherboard showing its long DDR2 colour-codes dual-channel memory slots (bottom right). Click on the image to view its full size


Crucial DDR2 RAM memory modules that fit into keyed DIMM slots on the PC's motherboard but only if it supports DDR2 memory

Crucial DDR2 RAM memory modules that fit into keyed DIMM slots on the PC’s motherboard but only if it supports DDR2 memory

SDRAM memory (Synchronous dynamic random access memory) evolved into Double Data Rate (DDR) SDRAM memory, which is now up to DDR4 (2014). Previous standards are DDR, DDR2, DDR3, which can all still all be purchased new from sites such as crucial.com by making use of its Crucial Advisor tool or downloading and running its Crucial System Scanner if you don’t know the information that the Advisor tool requires.

Note that each type of DDR/DDR2/DDR3/DDR4 memory comes in several frequencies, more commonly known as speeds. All of the modules have to be of the same speed in order for the memory to function at that speed. Installing a module with a lower frequency will make all of the modules function at the lower frequency. The settings for the memory are found in the computer system’s BIOS/UEFI but only if the motherboard’s manufacturer has provided them. Not all BIOS/UEFI setup programs provide settings for the memory. If made available, these settings, which include changing the frequencies and the voltages, should only be changed from their default settings if you know what you are doing. The motherboard’s manual for that make/model comes with the motherboard as a printed version or is obtained from the manufacturer’s website, usually in the PDF format that requires a PDF reader. These manuals almost always provide a section on the BIOS/UEFI.

Below are the names given to the different frequencies of DDR3 memory. The higher the frequency, measured in MHz, the faster the memory. As you can see in the table below, DDR3-800, also known as PC3-6400, has an effective data transfer speed of 800MHz. DDR3-2000, also known as PC3-16000 has an effective data transfer speed of 2000MHz, more than double that of DDR3-800.

The names given to the different frequencies of DDR3 memory

The names given to the different frequencies of DDR3 memory. Click on the image to view its full size.

Synchronous dynamic random access memory (SDRAM) –


DDR SDRAM – https://en.wikipedia.org/wiki/DDR_SDRAM

The computer’s motherboard must support the type of DDR memory in order to be able to use it, which means that the correct type of DDR memory has to be purchased for an upgrade or when building a PC from its components.

A motherboard outside its case with three RAM memory modules installed

A motherboard outside its case with three RAM memory modules installed in the DIMM slots. Click on the image to view its full size

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, DDR2, DDR3 and DDR4 memory modules. The correct type that the computer’s motherboard supports has to be used. Some motherboards can support two types, such as DDR3 and DRR4, 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 pair of Crucial DDR2 RAM memory modules

A pair of Crucial DDR2 RAM memory modules

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 on the How to install DDR/DDR2/DDR3/DDR4 RAM memory page of this website.

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

Corsair RAM memory module with a built-in passive heatsink

How To Replace Memory Heat Spreaders


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 motherboard with two SLI PCI Express slots and four DIMM RAM memory slots

The 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.

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.

A fail-safe way to get the correct memory

A fail-safe method of buying RAM memory is to visit crucial.com and make use of its Crucial Advisor tool if you know the required information, such as make/model of desktop or laptop computer or motherboard – or use its Crucial System Scanner that is downloaded and when run on your computer analyses it and suggest possible upgrades. You get your money back if the memory fails to work and shipping is free.

There is another relatively safe way to obtain a correct memory upgrade for a computer by using the part number on an existing module as a search query in a web-search engine. Click Laptop SODIMM memory modules to read the information on this page on how to do that with a SODIMM laptop memory module. The method can also be used to obtain desktop-PC memory. A search often leads to eBay. eBay sellers sell new or second-hand memory that is identified by part number that usually works – memory hardly ever fails and usually, but not always, lasts much longer than the computer it is installed in – but be sure to read the seller’s feedback, return policy and find out how much is being charged for delivery before making a purchase.

Multi-channel memory architecture: Dual-channel DDR3 and quad-channel DDR4 memory

In 2015, most laptop and desktop PCs come with between 4GB and 16GB of DDR3 or DDR4 memory or more, 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 7/8.1/10. A 64-bit version of Windows should have a minimum of 4GB of memory. A 32-bit version of Windows should have a minimum of 2GB of memory, but can use no more than 3.2GB, so not more than 4GB should be installed.

DDR4 SDRAM – http://en.wikipedia.org/wiki/DDR4_SDRAM

Eight quad-channel DDR4 kits reviewed: memory for Haswell-E –


Quadruple-channel (quad-channel) DDR4 memory has replaced DDR3 memory on the Intel Socket LGA2011 processor platform. DDR3 quad-channel memory is used in the AMD G34 (Opteron 6000-series server processors) platform and in the Intel LGA2011 platform. AMD processors for the C32 platform – the server processor socket for AMD’s single-processor and dual-processor Opteron 4000 series processors – and Intel processors for the LGA1155 platform employ dual-channel DDR3 memory.

Dual-channel and quad-channel memory is employed when two or four memory modules, respectively, with identical specifications are installed in DIMM memory slots lots on the motherboard that support dual-channel or quad-channel operations, which theoretically use both or all four modules as a group, respectively, theoretically doubling their bandwidth, but without adding much to performance – 5% to 10% at best. With two DDR4 memory modules are installed, they operate in dual-channel mode and in triple-channel mode with three modules installed.

The DIMM slots on the a PC’s motherboard are usually colour-coded to show which ones support multi-channel operation. The motherboard’s user manual, which provides information on which configurations and memory capacities can be installed, should be consulted to make sure that the correct memory is installed in the correct slots to achieve the desired modes of operation – single-channel, dual-channel, triple-channel and quad-channel modes. The user manual comes with a new motherboard or can be downloaded from its manufacturer’s website. If you don’t want to open a PC or laptop’s case to find out, the Belarc Advisor and CPU-Z, both free from their respective websites, can identify a desktop or laptop’s motherboard.

Multi-channel memory architecture –


Here is a webpage that is updated regularly on the best memory that is currently available:

Best Computer Memory –


RAM memory, which cannot retain its data when the computer using it is switched off, 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 SSD drives 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.

Direct Memory Access – DMA

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.”

RAM does not need a device driver

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.

Laptop SODIMM memory modules

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

4GB SODIMM laptop RAM memory module. Click on the image to see its full size

This is the part number on the Hynix laptop SODIMM module, shown above – 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 / 10 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 information 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 forum thread about matching modules using the part number:

Matching Modules for Dual-Channel –


How much memory do the 32-bit and 64-bit versions of Windows Vista / 7 / 8.1 / 10 need

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 Apple’s OS X or 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, many of which only came with 1GB of memory when Win7 was released in October 2009.

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. Windows 10 Home and Pro were released on July 29, 2015. Windows 10 – 32-bit and 64-bit versions – do not require any more memory to run than the same versions of Windows 7. 64-bit versions always require double the minimum amount of memory than 32-bit versions. In fact, memory management has constantly been improved since Windows 7, so Windows 10 runs better than Windows 7 on the same amount of memory.

I myself had a laptop and a desktop PC that ran 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.

32-bit and 64-bit Windows: frequently asked questions  [Win7] –


Most of the information on that Microsoft page can be applied to Windows 8.0/8.1 and 10.

As mentioned earlier, memory management has been improved in Windows 8 / 8.1 / 10, therefore those versions make better use of the same amounts of memory than Windows 7 does. They do not require more memory than Windows 7. I have a laptop that was new with Windows XP and 2GB of memory installed that runs Windows 10 Home version very well using MS Office, other applications and when accessing the web. However, if you want to play the latest PC games and perform other demanding tasks, such as video editing, you need a high-spec gaming desktop or laptop PC.

Up to 4GB of memory, the 64-bit versions of Windows require twice as much memory as the 32-bit versions, so the minimum a 64-bit version should have is 2GB for Windows 7/8.1/10. Most computers in use currently use a 32-bit version of Windows, but almost all recent or new PCs come with a 64-bit version.

Note also that even with a 64-bit processor and a 64-bit version of Windows 7 / 8.1 / 10, 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.

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?


Note well that the new AMD and Intel processors that have integrated graphics chips to render their computer’s graphics 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 Fusion processors (APUs), which all have onboard graphics chips. A 64-bit operating system is required to use more than 3.20GB of memory, which for most users means having a laptop or desktop PC running the 64-bit versions of Windows 7 / 8.1 /10. The following article reviews seven 8GB memory kits:


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

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 Advisor tool on crucial.com if you know the make/model of the PC or laptop or motherboard, or the Crucial System Scanner if you don’t know that information, 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.

Low quality RAM and mixing brands 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 Advisor tool, 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.

Registered and ECC RAM memory

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.

UEFI/BIOS RAM memory settings taken from the BIOS section of a motherboard’s user manual

The UEFI/BIOS of  the motherboard of a PC provides settings that vary from motherboard to motherboard.

Changing the settings for the RAM memory is possible to the extent of the settings that the system UEFI/BIOS provides.

It is always best to leave UEFI/BIOS settings at their defaults or optimized settings

Note that it is always best to leave UEFI/BIOS settings at their defaults or optimized settings.

I know from experience that it is always best to leave these settings at their defaults or optimized settings. Using alternative settings is seldom worthwhile unless you are using a temporary setting to fix a problem, such as one known as “Reset data configuration” that resets the BIOS if conflicting settings make the operating system fail to boot and then turns itself off. You could also enable a particular setting to get specific hardware to function, such as enabling the AHCI setting to make an SSD drive work.

OCZ SSD drive not recognised by BIOS & Windows 7/8.1/10 install –


Overclocking memory – UEFI/BIOS settings that overclock components

If a motherboard is designed to make overclocking of the processor and RAM memory, the full range of settings that make overclocking possible – running components faster than their stock speed – will be available.

RAM Overclocking Guide: How (and Why) to Tweak Your Memory [August 2016] –


The motherboard of PC workstations have fewer customisable UEFI/BIOS settings in general and for the memory. Laptops usually have the fewest customisable settings. The reason being that if the user enables conflicting settings, the computer may fail to boot and cause support costs.

People who intend to overclock their computers either find out how to do it or already have the knowledge. Overclocking is definitely not something to jump into without doing plenty of research first. Overclock the processor or memory too far and you could destroy them and maybe the entire motherboard.

Below are the extracts from the UEFI BIOS section of the user manual of a motherboard made by Gigabyte, showing the settings for the memory.

UEFI/BIOS memory settings from the BIOS section of the user manual of a motherboard made by Gigabyte

Additional UEFI/BIOS memory settings from the BIOS section of the user manual of a motherboard made by Gigabyte. Click on the image to view its full size

UEFI/BIOS memory settings from the BIOS section of the user manual of a motherboard made by Gigabyte

UEFI/BIOS memory settings from the BIOS section of the user manual of a motherboard made by Gigabyte. Click on the image to view its full size