Exactly as the title says, its a 512MB SDRAM stick of PC133. CAS Latency is 3 at PC133, 2 at PC100. Will trade for a stick of 256MB PC100 SO-DIMM for my iBook G3. Tested the SDRAM in a AGP G4, worked perfectly under OSX and OS9 and passed all the tests. Tested in an Athlon XP machine with Memtest, it passed. Will also trade this and 2 256 MB PC133/100 sticks of Crucial CAS2 RAM for a 512MB SO-DIMM. Can also turn this into 2 256 MB Crucial DIMMs for all of you that have G3 machines. Thanks for looking everyone! EDIT : The 2 Cruical DIMMs are claimed. Thanks Rob! I have more 256 MB DIMMs btw, Kingstons. Lots of them. I need SO-DIMMs also for some PC laptops I was given.