Actually, if you =really= want to get into the nitty gritty, throw these into the mix as well... PCI-E. DDR-333 and 400 DDR-2 SATA BTX form factor X86-64 AMD's single channel Athlon 64, dual channel Athlon 64, Intel enabling the pseudo 64 bit junk (more accurately a 40 bit bus with multiplexer). USB 2 Nforce 3 and 4 chipsets Via K8T800 and 890 chipsets At least 2 generations of Geforce class video chipsets At least 2 generations of ATI's GPU offerings. Going from AGPx2 to AGPx8 to PCI-E16 And that is just off the top of my head.