Hello all - I have inherited two PowerMac G4 450 MHz AGP machines for use at the non-profit arts organization that I help run. I believe these are either the "Sawtooth" configuration ( http://www.lowendmac.com/ppc/g4saw.shtml ) or the "Mystic" configuration ( http://www.lowendmac.com/ppc/g4mp.html ), probably the former. They each came with two 128 MB DIMMs (256 MB RAM each), which is anemic of course, so I bought two DIMMs of 512 MB RAM of the same type, intending to add one to each machine. Same bus speed (133 MHz) and voltage configuration (contact edge indents) as the existing memory. There are 4 DIMM slots. The DIMMs go into the slot just fine, but are not recognized by the system. It boots up as if they aren't there; there are no abnormal boot beeps or flashing power button. It just doesn't count them as existing in the RAM pool (per "About This Mac"). I did try both DIMMs all by themselves, separately in the first slot and together in the first two, and those boots failed with the warning beep, flashing power button, and no video. I can take these back to the vendor (a trusted local whitebox shop) and have them test them, but is there something special that I need besides PC133 SDRAM? I noticed that these new 512MBs are 16-chip DIMMs, and the existing 128MBs are 8-chip DIMMs. Does that matter? I vaguely recall that there's a difference between 16-chip and 8-chip. Thanks!