Some memory might have a little better performance or reliability than another compatible memory. When you buy memory just ensure it has some kind of warranty to permit returns or exchanges if something happens or the memory is bad when it arrives.

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Adding memory should be very simple, but many vendors leave out critical information necessary to making your decision.

Some motherboard vendors place restrictions on the types of memory within the specification as they squeeze out as much performance as possible or as cheap a board as possible.

Things to watch out for:
– Size of memory module – can your system take a 1 GB, 2 GB or 4 GB module?
– Type of module – DDR, DDR2, DDR3, etc
– Memory Module form factor: 184-pin, 168-pin, 240-pin and notches
— Dictated by type of module
– Module shape (could be low profile)
– Type of memory on module (ie: 256 x 72)
— How much memory the individual chips hold
– non-ECC vs ECC
– Speed – PC3-12800 or DDR3-1600 which supposedly “mean” the same
(But various vendors are fuzzy on speed representations)
– Banking (single, dual)
– CAS / CL / Latency (ie: 8-8-8-24 and sometimes expressed in a more detailed format)
– Unbuffered / buffered
– Registered
– Voltage

One other thing is most boards will work with memory rated a step or two faster than specified but the memory modules in some cases do not work when clocked down to the motherboard specification. Even major vendor memory modules can exhibit this behavior.
ie: PC 1800 memory for a PC1600 system. Most times it works.

(dyslexic typing corrected)