Crumb wrote:
"Only Opteron has HT at the moment - but IBM have just joined the HT forum :-)"
oh, I thought that the 970 used Hypertransport... sorry
The G5 uses the proprietary ApplePI/Elastic Bus/whatever the heck it is between the CPU and the offboard memory/system controller.
The system controller (practically, the 'chipset') then hosts a HT link or few that allow the use of commodity PCI-X bridges and integrated-peripheral chips ("southbridges," though that term seems to be wearing thin). I don't know if Apple is actually using commodity parts for these now, but this reserves them the option, and/or keeps any custom work they do in that domain 'standard' enough that it could be licensed for others' designs (or just coexist with later iterations of their product line - who knows what the useful life of the 970's bus will actually be, and/or if it'll get replaced by HT at some point?)...
So anyhow, the 970 itself doesn't use it, but the Macs do, and it's hard (not impossible, but hard- you'd have to cram all your PCI-X and whatnot the same chip, and hope you can find something better than the 686B to use for the onboard peripherals people expect) to imagine a system hub without it, for desktop purposes at least. Maybe if those sorts of peripheral chips do show up, or someone licenses V-Link or something weird, instead...
http://www.apple.com/powermac/architecture.html
