“There is always confusion when choosing an upgrade in memory RAM modules, whit so many different names, connections, pins etc. What makes a module different from another? How do we know which module is good for our PC and which one would not fit or would fit but not work at all?”
Below is a full explanation to all this different memory module types but first of all let’s make a distinction and split the Memory RAM in two main categories. Let’s call the firstDesktop, (includes Home/office PC and laptops) and the second Server, (Includes all the enterprise branch of servers and virtual machines).
Desktop RAM
Most desktop personal computers require Non-ECC Unbuffered RAM. There can be exceptions, so use the information below to determine what memory type your machine is currently running.
Non-ECC unbuffered memory usually has 8 chips per side and can be single sided or double sided. Low density dual channel desktop RAM commonly has 8 chips on both sides.
Server RAM
Server RAM is ECC Registered, does not work in most desktop computers
Error Checking and Correction (ECC) memory is mostly considered essential in enterprise environments these days. Error checking and correction allows for single bit errors to be both detected and corrected when they occur. When a single bit error is detected, the parity information is used to reconstruct the data with an error. This function might slow down the actual RAM speed of 20%, however most of the server can handle much higher quantities of RAM Modules.
Desktop RAM usually needs to be Non-ECC and Non-Registered (unbuffered).
For desktops, error correction is less important as a lot of figures put single-bit errors in the range of 1 per 1GB or 1 per 2GB of memory each month. To a desktop user, this may cause a program to crash, or at worst require a reboot.
Desktop RAM
(DIFFERENT TYPES)
• Desktop SDRAM – 168 pins, 2 notches at the bottom, (PC100 or PC133)
• Desktop DDR – 184 pins, 1 notch at the bottom, (PC2100, PC2700 or PC3200).
• Desktop DDR2 – 240 pins, 1 notch at the bottom. The notch in DDR2 RAM is in a slightly different location to prevent it from being installed in machines that require DDR RAM. DDR2 is not backwards compatible with DDR1.
• Desktop DDR3 – 240 pins, 1 notch at the bottom. The notch in DDR3 RAM is in a different location to prevent it from being installed in machines that require DDR or DDR2 RAM. DDR3 is not backwards compatible with DDR2.
Laptop RAM
(DIFFERENT TYPES)
Laptop computers require Non-ECC Unbuffered SODIMMs. The module size is physically about half as long as desktop memory.
• Laptop SDRAM – 144 pins, (PC100 or PC133).
• Laptop DDR (DDR1) – 200 pins, (PC2100, PC2700 or PC3200).
• Laptop DDR2 – 200 pins. The notch is in a slightly different position to prevent DDR2 RAM from being installed in DDR1 laptops. DDR2 is not backwards compatible with DDR1.
• Laptop DDR3 – 204 pins. DDR3 is not backwards compatible with DDR2 or DDR1.
Server RAM,
(ECC REGISTERED)
Server memory is generally ECC Registered (buffered). There are extra chips on the module that provide error correction and data checking functions. It is easy to spot ECC Registered Server RAM by looking at the chips on the module.
While desktop memory usually has eight chips per side, server memory has 9 large or 18 half-size chips per side, plus two or three smaller “register” chips. The 9th (and 18th) DRAM chips provide the error correction function, and the additional “register” chips hold the data for one clock cycle (ie act as “buffers”) to increase the reliability of high-speed data access.
Unless a machine specifically supports ECC Registered memory the machine will not function correctly and may not even boot with this type of memory installed.
Server RAM,
(ECC UNBUFFERED)
Many workstation computers and some servers use ECC unbuffered RAM. ECC unbuffered RAM looks similar to standard desktop memory, but instead of 8 chips per side it has 9 chips per side. The 9th chip handles the error correction function in machines that support ECC memory.
It can be confusing because server RAM is often referred to as simply “ECC RAM”, but ECC unbuffered is not the same as ECC registered. If a machine uses DDR2, DDR, or SDRAM and requires ECC unbuffered memory, in most cases ECC registered is not compatible. Server motherboards that use DDR3 memory can often use either ECC unbuffered or ECC registered, however you cannot use both types in the same machine at the same time.
Server RAM,
(ECC FULLY BUFFERED)
FB-DIMMs (fully buffered) are a type of ECC RAM which use an Advanced Memory Buffer (AMB) between the memory controller and the memory module. The notch on FB DIMM memory is offset to prevent these modules from being installed in systems which use standard DDR2 RAM. Future development of this memory type is uncertain and are less commonly used.
To be absolutely certain what memory type a machine requires, it is suggested to look at the memory currently installed or check the product manual.
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