Which kind of DIMM memory does my computer use?

[bartthecartoon]

I have an e-Machines T3990 (desktop), and in my manual it told me how to install more memory, but all it said about the type of memory was that it takes DIMM. I have heard that there are different kinds of DIMM. Which kind am I supposed to buy?

 

[chickenfoot]

go to www.crucial.com and follow the 'find your memory' steps