---------- On July 20, 1998 John Rinehart wrote: To go back to the original question that I asked, I would like to upgrade the memory on an older Packard Bell system. The system has an AMI MB and BIOS. The chipset on the MB is an Intel Neptune chip set 82433NX (LBX), 82434NX (PCMC) , and 82378ZB (SIO.G). Information in Packard Bell's WEB site states for this system PB550: 1. SIMM speed must be 70ns or faster. 2. The SIMMs are 72-pin and can be x32 or x36. The motherboard design does not require parity checking The motherboard will not use EDO, only Fast Page Mode SIMMs will operate correctly in this motherboard. And yet Scott Mueller's Upgrading and Repairing PC's states on page 803 paragraph 2 of the 8th edition, "You can install EDO memory in older systems that do not support it because EDO is backward-compatible with standard (called fast page mode) memory." Sincerely, John I can't argue with your experts, but I have never had a motherboard pass the POST test with EDO accidently installed when the motherboard specifically stated fast page mode ram was required (and I have accidently done this too often, I admit.) However, there are such things as auto sensing SIMM sockets, and I have several Pentium boards using the VIA VPX / 97 chipset that can use mixed edo and fast page as long as it is installed in pairs. I also have two Taiwanese 486 socket 3 boards of no brand name that I bought from an OEM and they support EDO and fast page mixing. Like most 486 boards the simms do not have to be installed in matching pairs. Tom Turak