The architecture of the SiS648 northbridge is very similar to that of the
SiS645. The main difference here is that we now have support for 8X AGP
graphics cards, and a PC3200 memory divider. The Northbridge connects to the
Southbridge via a direct 16 bit bridge running at 533 MHz and offers a total
bandwidth of 1 GB/s. On this board the SiS 648 chipset was of the "A2"
Unofficially, the SiS648 also supports PC3200 (DDR400) memory. We tried to
test this out with but were not able to get the Abit SR7-8X to run with any
or the memory we tried (no matter what memory timings used) at 400 MHz FSB.
The SiS648 chipset itself is a little toasty after a few hours of
use, and even though the passive green heatsink can cool the Northbridge, it would have been
nice to see some form of active cooling on it.
Our first 648 motherboard, the MSI 648 MAX
wasn't the greatest of overclockers. It hit the wall at 143 MHz FSB, and stubbornly refused to budge an inch
after that with the gear we used. Whenever we review Abit boards we usually
expect them to be pretty good overclockers all things considered.
Knowing that the test Pentium4 1.6A can
do 2.4 GHz easily, the first FSB setting I tried was 150 MHz. There was no POST.
Feeling a bit discouraged, I played with the memory timings and voltages to
try and get it to work, but it was all for not.
Lowering the FSB to 145 MHz didn't help, neither did 143...
Finally at 140 MHz the system POSTed and booted into Windows for the first time.
After a few more tries we settled for a 141 MHz FSB overclock. That is
a bit discouraging, but then again overclocking is luck of the draw isn't