What kind of RAM goes in your Mac? Look for the picture
that represents your Mac. Typically you can use faster RAM
that what is supposed to go inside your Mac. For example,
if your Mac takes 266 MHz PC2100 RAM, you can install 333
MHz PC2700 RAM without any issues. The RAM will throttle
down to the correct speed. However, if your Mac takes PC133
RAM, you cannot install DDR, or DDR2. The same is also true
for other types of RAM. You have to stick with the type of
RAM your Mac takes. Its also not recommended to get slower
RAM than what your Mac takes. So for example, if your Mac
takes PC3200 DDR RAM, don't install PC2700. All of the RAM
regardless of the speed will throttle down to the slowest
speed RAM. The same is true for the different types of DDR
RAM, DDR2 RAM isn’t backwards compatible with DDR RAM
and DDR3 RAM isn’t backwards compatible with DDR2 or
DDR RAM. What ever type of DDR RAM your Mac may take is the
type of RAM you have to buy.
Its recommended that you stick to known brands of RAM.
Don't install generic RAM into your Mac. You may be able to
get away with it, but your milage will vary. Good brands to
stick to are, Samsung, Hynix, Crucial, Kingston, Edge, and
Mushkin.
If you're still not sure what RAM to get after looking
through these pages, click the Help link in the menu above,
fill out the small form and I'd be glad to help you out.