updated mar2015

RAM has different type, speed and latency:
- TYPE is mostly how many times data is read (or written) during 1 clock cycle; DDR transfers data 2 times per clock cycle, DDR2 does it 4 times, DDR3 8 times.
- there are special types for servers and workstations, that have built-in error correction; these are ECC types, and have different "RANKS" that you have to be aware of! Normally single rank and dual rank can be used on the same motherboard and in the same memory channel, but since dual rank has more chips and thus normally higher capacitive load they have to mounted in the slots farthest away from the CPU.
- there are also even more special types for servers, called "ECC REGISTERED". Those types have an extra buffer between the channel bus and the memory chips, which makes it possible to use a high amount of RAM blocks. They will only work in hi-end machines like the epic HP-Z800, and cannot be mixed with non-registered types.
- SPEED is number of bits or Bytes (1 Byte is 8 bits) per second.
- LATENCY is how much time there has to be between subsequent read/write cycles.

RAM versions.

type data rate name speed
SD 100MHz PC100 100x64/8=800MB/s
SD 133MHz PC133 133x64/8=1066MB/s
RDR (RAMBUS) 2x400=800MHz PC800 800x16/8=1600MB/s
DDR 2x133=266MHz PC2100 266x64/8=2100MB/s
DDR 2x167=333MHz PC2700 333x64/8=2700MB/s
DDR 2x200=400MHz PC3200 400x64/8=3200MB/s
DDR2 4x133=533MHz PC2-4200 533x64/8=4264MB/s
DDR2 4x167=667MHz PC2-5300 667x64/8=5333MB/s
DDR2 4x200=800MHz PC2-6400 800x64/8=6400MB/s
DDR3 8x100=800MHz PC3-6400 800x64/8=6400MB/s
DDR3 8x133=1066MHz PC3-8500 1066x64/8=8528MB/s
DDR3 8x167=1333MHz PC3-10700 1333x64/8=10664MB/s
DDR3 8x200=1600MHz PC3-12800 1600x64/8=12800MB/s
DDR3 8x233=1866MHz PC3-14900 1866x64/8=14928MB/s
DDR4 8x333=2666MHz PC4-21300 2666x64/8=21333MB/s
DDR4 8x400=3200MHz PC4-25600 3200x64/8=25600MB/s

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Testing your RAM for errors.

When there is something wrong with your RAM, you can experience many weird crashes.
In that case you can do a test of your RAM.
There is a nice program called "Memtest86", that you can burn on CD, boot with, and run a long test.
The official version also has a free edition, that can be found here: link.

In W7, there is a built-in memory test tool in the toolbox.
You can use it when you click F8 during boot of windows > Repair my Computer > Memory Diagnostics

The biggest challenge of this tool is, that you only can see the results via "Event Viewer".
The following screenshot shows how to do it, starting in ControlPanel:


upgrading RAM.

First, check what RAM you have by using CPU-Z or SIW see here
You would like to upgrade with the same sort of RAM, and it is normally a good idea also to check with the motherboard vendor what the recommended types are.
Then, locate the memory in your PC.

changing laptop RAM

Use both hands (only shown for left hand here):


When placing the new RAM, be sure to push the module completely into the socket before pushing down into the clamps.

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