BloodyIron :
I've been trying really hard to find a guide which outlines all the different technologies I need to know for modern DDR3 server RAM. I could swear I saw one on tomshardware's site, but I can't find it there, and I can't find one on other sites like anandtech. Can someone point me to such an article please? The more depth the better.
Most modern servers will take pretty much any kind of DDR3 RAM, unlike older servers which took only registered ECC RAM. I do not know of a comprehensive guide to server RAM that is not specific to a certain server or a sever CPU so I will give you a brief overview.
There are four main types of DDR3 server RAM:
1. Unbuffered non-ECC RAM. This is the same kind of stuff as you use in a desktop. Maximum sizes at the moment are 8 GB/DIMM (will be up to 16 GB/DIMM with the final 8 Gb DDR3 ICs) and up to two DIMMs/channel. The advantage of this stuff is that it is inexpensive and if you are enterprising, it can have better performance than any other kind of DDR3 especially if you are handy with an EEPROM flasher and use low-latency 1.50 V desktop DDR3. The disadvantage is that there is no error correction and that can lead to shorter uptimes and possibly data corruption although unlikely.
2. Unbuffered ECC RAM. This has the same module sizes and number of DIMMs as unbuffered non-ECC but adds a ninth memory IC per rank and has the same error correction and stability as "real server (registered) memory) but with slightly higher performance and lower cost. Unbuffered ECC memory was historically used as workstation memory where you needed more reliability than a typical desktop but were not using server hardware which required much more expensive registered memory.
3. Registered ECC RAM. This is not compatible with any of the unbuffered types due to the presence of a little memory buffer which holds all memory requests for a clock cycle. (You can use either type of unbuffered memory *or* registered ECC but not both at the same time.) The buffer allows for much larger quantities of memory per module (currently 32 GB/module) due to the ability to run 4-bit wide ICs rather than 8-16 bit wide ICs as required by unbuffered RAM and also the ability to run four ranks of memory vs. one or two. Registered RAM can also support up to three DIMMs per channel as opposed to two with unbuffered. It is somewhat slower than unbuffered RAM and usually quite a bit more expensive. This is "server RAM" as the old grayhairs know it and what all servers used to require until the DDR3 generation.
4. Load-Reduced DIMMs (LR-DIMMs.) An offshoot of registered ECC, this allows for even larger memory quantities per DIMM than registered ECC. Only supported by the later generations of DDR3-using servers (IIRC Opteron 4200/6200 and later, Intel Sandy Bridge LGA2011 and later.)
If you have any questions about what memory is supported by any particular machine, feel free to ask.
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