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Date |
: Apr 2nd, 2002 |
| Category |
: Chipset |
| Manufacturer |
: Various |
| Author |
: Jin-Wei Tioh |
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SiS came into the Pentium 4 chipset market from out of nowhere, blind-siding quite a few parties (yours truly included). Without warning, I received a reference SiS645 motherboard together with a stick of Micron DDR333 memory marked "Engineering Sample". This is probably one of the most exciting chipsets of the year, and with good reason. What with the good performance reputation of the SiS735 and SiS745 Socket-A chipsets, many wonder just what SiS can do in the Pentium 4 chipset arena.
As mentioned earlier, SiS has a Pentium 4 bus license, which puts them in a much better legal position than VIA. On paper, the SiS645 looks absolutely fabulous. A two chip solution with the 645 North Bridge, and the 961 South Bridge, offering 6 USB ports and ATA-100 support. It's made special by its memory controller - an advanced version of the one in the SiS 735. What's so special? It officially supports the operation of the memory bus at 166MHz, ie. DDR333 with a maximum memory capacity of 3GB. This gives the Pentium 4 2.7GB/s of peak memory bandwidth, still shy of 3.2GB/s, but better than the 2.1GB/s offered by DDR266. Like the i845 and P4X266, the 645 supports the asynchronous operation of the FSB and memory buses with three different settings : 100/100, 100/133, and 100/166MHz. The North and South Bridges are interconnected with SiS's MuTIOL technology. It is a 16-bit wide bus clocked at 266MHz, designed for multiple isochronous virtual channels. Thus, it is able to offer a peak bandwidth of 533MB/s both upstream and downstream, being the most advanced chipset interconnect on the market so far. Although it is questionable whether such a large headroom is required, there's no harm done.
Incidentally, to make the 645 more attractive for OEMs, it is pin compatible with the forthcoming 650 North Bridge. The SiS650 is basically just the SiS645 with integrated SiS315 video.
Our SiS645 test platform is the reference motherboard supplied by SiS. The board was not only shocking because it supported DDR333, but because it was too large to meet ATX specifications. Outfitted with 6 PCI slots, 1 ACR slot and 1 AGP slot, it has one slot too many to fit in any ATX case. An interesting observation is that both the North and South Bridges lack any cooling solution whatsoever. We performed several stability tests to verify its stability, and the board remained stable even after going through several "makeworld -j4"s under FreeBSD.
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