I'm running Windows 7 64 bit. The first RAM I tried was from KomputerBay (found on Amazon). While it worked in that the PC booted up and ran OK for a while, it would randomly cause a BSOD. I used MEMTEST86 to test the RAM and it passed but the tests but still caused a BSOD after some time. So I sent it back. I then purchased some Patriot RAM from Fry's (FRYS.com #6416292) and haven't had any issue at all. I also put a Cosair Force 3 120GB SSD in at the same time. Since it generates no heat (the regular HDD generated quite a bit) maybe that helps the RAM not heat up? I don't know but it is an additional change. The next thing I'm going to upgrade is the processor. I'll install a 65W quad core and that should make this PC good to go for the next 3-5 years.