The architecture of the SiS648
northbridge is very similar to the SiS645 - the main difference here is the
support for 8X AGP graphics cards and the 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.
Unofficially, the SiS648 also supports PC3200 (DDR400) memory. During the
testing of this board we didn't experience any problems running the system
with Corsair XMS3500 CAS2 at DDR400 mode.
As I alluded to before, other SiS 648
motherboards which have come across the test bench were never that great in the
overclocking department. From what I have seen around, most other hardware
reviewers have seen similar limits to their overclocking success. Never one
to let tradition get in the way, we began to overclock the 4SDA5+ with low
FSB's. To our surprise we quickly passed the 143 MHz mark. Increasing
the FSB further led the system to 153 MHz where we had to up the CPU
Vcore to 1.6V to stabilize the situation.
To hit 160 MHz FSB, the system needed yet
another increase in Vcore, this time to 1.65V. At any FSB's higher
than 160 MHz the system would crash during SysMark2002 in the Internet Content portion of the
benchmark. Still, 160 MHz is pretty good for a SiS648 based motherboard!