W.x. wrote on 2021-03-06, 06:06:

So, what is latest SIS chipset, that supports Universal AGP (3.3v signaling), as far as I see, SIS 645dx is ok, but doesnt support 800 Mhz FSB and HT, and Prescott CPUs.
651 seems same as 645dx, only better integrated graphics? Also built in support for USB 2.0. What about 648fx? This supports HT for sure, 800 Mhz p4 too, but not sure if there are some boards, that supports Universtal AGP 2x,4x, so 3.3 v signaling. Because Asus P4S800 doesnt support it, only 1.5v AGP cards. Not sure, if this apply to all 648fx motherboards.
Anyway, what's last SIS chipset for P4, that can support AGP 2x 3.3v cards?

Iv got a 645 chipset that only takes 533fsb Northwood CPU's and doesnt support HT with a universal AGP Pro slot. It actually takes the 3.06ghz Northwood just without HT. So the 645dx will actually work with the same chip and HT enabled. EDIT: Apparently it's only the B stepping of the 645dx chipset that allows HT and you also need a bios with HT support after reading a couple old Overclocker's forum threads.