1GB Kit 2 X 512MB DDR2 Memory for Dell Optiplex GX280 SX280 GX280n GX320 GX520 GX620 GX620N Desktop PC2-4200 240 pin 533MHz DIMM RAM (PARTS-QUICK BRAND) Speed: PC2 4200 533MHz Form Factor: 240 pin DIMM Capacity: 1GB Kit 2 x 512MB Warranty: Lifetime