Full Details on Amazon.com : http://www.amazon.com/gp/product/B001V6O40O?tag=tsukuyomi-20

4GB kit (2GBx2) Upgrade for a Dell OptiPlex GX620 Series (Desktop Mini-Tower and Small Form

240-pin DIMM
DDR2-667
DDR2 PC2-5300 Unbuffered NON-ECC DDR2-667 18V 256Meg x 64
The only brand of memory upgrade available directly from a DRAM manufacturer tested to meet the most stringent industry specifications
Install it yourself in about 15 minutes The same top-quality memory that the worlds largest computer manufacturers install in the systems they sell