The SiS 648FX was the first chipset to come out supporting DDR-400 and 800MHz FSB that was independent; that is, not made by Intel. The 648FX is a direct descendant of the original 645 chipset, the first DDR supporting chipset commercially available. This chipset predated the i845D series, however, never got the full attention it deserved. Today SiS has put all on the line to take on the budget users.
The 648FX chipset is comprised of the 648FX HMAC and the SiS 963 or 964 MuTILO Southbridge. These two are interconnected by a 16-bit bus operating at a peak bandwidth of 1GB/s, the fastest of all the busses available. Designed to take full advantage of single channel DDR, the 648FX takes a page from the 655FX's book with its new bus optimizations called Hyperstreaming.
The Hyperstreaming engine: Its design is simply a packet sending technology. Instead of sending one large chunk of data at a time, it allows concurrent smaller transfers to take place allowing the reduction of latencies between memory, AGP, PCI and CPU buses. While this may not seem like a huge advantage, when you are limiting the memory bandwidth you will need all the optimizations you can get.
The DDR memory controller is a direct descendant of the original 648 in that it supports DDR-266, 333 and 400 technologies. This allows for a maximum of 3.2GB/s of memory bandwidth transfer. Hyper-Threading is also supported on this chipset. Hyper-Threading has been implemented on SiS chipsets since revision 2 of the 645 series when Intel first announced HT.
The Southbridge mostly widely used is the 963(UL) due to the higher costs involved with the 964 series. The 963(UL) brings ATA-133 IDE, six USB 2.0 ports, 10/100 Ethernet, AC'97 2.2 audio as well as Firewire support.
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