I have a Dell Inspiron 580 computer running Windows 7 Home (64 bit). There are currently 2 (1 gig sticks of memory). I want to add two more gigs of memory for a total of 4 gig. Do I buy a single 2 gig stick, which means I have three sticks of memory for a total of (4 gig) OR, should I buy 2 (single gig sticks) which means I now have 4 sticks of memory, and a total of 4 gigs. Many thanks, Mike

it seems you can do both : http://support.euro.dell.com/support/edocs/systems/insp580/en/sm/memory.htm#wp1181032

Thanks allen2----but which would give the best performance. Adding 2 (1 gig sticks) or just adding a single 2 gig stick ?? if the answer is to add a single 2 gig stick, I assume I should put in into DIMM1 slot ??

The best peformance should be done in dual channel configuration so with 4x1GB modules.

yes, #4 is right.