"Mr. Geeky, you sold me bad RAM! I put it in my computer and it just beeps! I'm going to come over there and break your legs!"
FACTOID: The #1 cause of returns at GeeK NoiZe is that people buy ECC Registered Server RAM for incompatible desktop or workstation machines.
For example, the kind gentleman quoted above, who it turns out purchased server memory for his desktop machine. The computer beeped not because the RAM was defective, but because the memory was incompatible with his computer.
So let's talk RAM and see if we can shed some light on this murky and mysterious subject.
TYPES OF COMPUTER MEMORY:
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.
Please note that server RAM does not work in most desktop computers. Server RAM is ECC Registered, and desktop RAM usually needs to be Non-ECC and Non-Registered (unbuffered).
• 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
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
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 computers require Non-ECC Unbuffered SODIMMs. The module size is physically about half as long as desktop memory.
• Laptop SDRAM - 144
(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.
ECC Registered Server RAM
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 your machine specifically supports ECC Registered memory your machine will not function correctly and may not even boot with this type of memory installed.
ECC Unbuffered RAM
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 your 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.
To be absolutely certain what memory type you are running, look at the memory currently installed in your machine and check your product manual.
ECC Fully Buffered Server RAM
FB-DIMMs (aka 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.
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