desktop non-ecc 240 pin ddr2; I suggest you pull out one of the sticks and see what brand and speed they used. Could be pc5300 (667) or pc6400 (800). Can't tell the max per slot, but look for some 2x2 gb on craigslist. If you already have 2 gb, I would do a search for dell specs and download the manual. The board may not recognize 4 gb of ram; also windows 32 bit only recognizes about 3.25 gb out of 4, so the upgrade may not be worth it. Also, don't get 1066 ram; the dell bios won't run your board at the higher speed, and may not even post.