The original SiS 645 took the Pentium 4 market by storm. It took SiS from the bargain basement into prime-time, and enthusiasts took notice. At the time Intel was still behind Rambus RDRAM for their flagship 850 chipset, and they were just barely starting to test the waters for DDR on the P4 platform, which gave the 645 a market of its own. (The P4X266 doesn’t count). As Intel dumped RDRAM and decided to get into high performance dual channel DDR with the E7205, SiS again came up with a low cost alternative, the dual channel 655. SiS’s first attempt to counter the 865\75 with 800mhz fsb is the curiously single channel 648FX, which we will be looking at today.
Here are the specifications of the new chipset:
• Host Interface Controller
o Support Intel Pentium® 4 HT 800 CPU
o Support Intel Hyper-Threading Technology
o Support 800/533/400MHz Front-Side Bus • Integrated High Performance Dual Memory Controller
o Up to 2 DIMMs of DDR400, up to 3 DIMMs of DDR333/DDR266
o Support Un-buffered DDR DIMM and up to 1GB per DIMM
o Suspend-to-RAM(STR) • Support AGP 8X Interface
o Support AGP 8X/4X Interface
o Support Enhancements of AGP v3.5 Register Format
o Support Fast Write Transaction • MuTIOL 1G® Delivering 1GB/s Bandwidth
o Proprietary Interconnect between SiS648FX and SiS963L
o Bi-Directional 16-bit Data Bus at 533MHz Operating Frequency
o SiS963L MuTIOL 1G® Media I/O • USB 2.0/1.1 Host Controller
o One EHCI USB 2.0 Controller and 2 OHCI USB 1.1 Controllers
o Support Total 6 USB 2.0/1.1 Ports
o Support USB 2.0 High-Speed Device @480 Mb/s Transfer Rates • Fast Ethernet/Home Networking Controller with MII Interface
o Support 10/100Mb Fast Ethernet or 1/10Mb HomePNA 2.0 with External PHY • Audio/Modem Controllers with AC’97 Interface
o AC’97 v2.2 Compliant
o Support 6 Channels of AC’97 Speakers Out and v.90 HSP Modem • Advanced Power Management
o ACPI 1.0b and APM 1.2 Compliant • Dual IDE Channels with Parallel ATA 133/100/66
• Support Up to 6 PCI Masters
• LPC 1.0 Interface
• Integrated RTC
• Integrated Keyboard/PS2 Mouse Controller
• PC2001 Compliant
• SiS180 Serial ATA Host Controller
o Support Two Independent Ports of Serial ATA 150
o Support Dual IDE Channels with Parallel ATA 133/100/66
o Support PCI Rev 2.3
o Software RAID Function Support
o Support RAID0, RAID1, RAID0+1 and JBOD Function
Similar to the nForce2 Ultra400, the SiS 648FX is based on the 648, just with a few updates, a bit of a performance boost, and official support for 800mhz bus Pentium 4 processors and DDR 400. The North Bridge supports up to 3 DIMM slots for a maximum of 3GB of ram, though only two slots can be used with DDR 400. The 648FX has a slight advantage over the i845PE in this area, which could only support a maximum of two double-sided modules. The newer 865 and 875 support a maximum of 4 double-sided modules. Of course what stands out most on the feature list is the lack of dual channel DDR capability. It’s curious as to why the 648 was given 800mhz fsb support, and not the newer dual channel 655. My only guess is that SiS is still working on the update for the 655.
Update: After talking to SiS, I learned they currently do have a 655FX in the pipeline, which will be released after the 648FX. Stay tuned for an SiS 655FX preview.
