X-bit labs

SiS655 - New Dual-Channel Chipset. Gigabyte GA-8SQ800 Ultra – First SiS655 Based Mainboard

Category: Chipsets

by Ilya Gavrichenkov

[ 03/21/2003 | 01:49 AM ]

Following in Intel’s footsteps, SiS Company started using dual-channel memory controllers in Pentium 4 chipsets. Their first product with the dual-channel controller, SiS655, supports DDR400 and has every chance to become one of the fastest Pentium 4 chipsets. Will it succeed?

Table of contents:

• Closer Look at SiS655
  
• SiS655 against Intel Chipsets: Specification Comparison
  
• Closer Look at Gigabyte GA-8SQ800 Ultra Mainboard
  
• Testbed and Methods
  
• Performance
  
• Conclusion
  

Dual-channel chipsets continue conquering the market. After Intel transferred its processors to the Quad Pumped Bus, the CPU bus bandwidth sprang up and much faster memory types became necessary to use it efficiently. As CPU speed grows much faster than memory speed, developers have to bring about new technological solutions to create well-balanced computer systems. The most popular solution like that now is the implementation of two memory controllers working in parallel. As a result, we get twice the memory bandwidth.

The first desktop chipset to use this solution was i850 supporting RDRAM. Although this memory type can’t boast very high bandwidth, it nevertheless allows easy implementation of dual-channel access due to the relatively narrow memory bus. However, RDRAM technology is getting quite obsolete nowadays, at least in desktop PC market. That’s why the developers are working hard on dual-channel solutions involving the pretty widely spread DDR SDRAM. Although the bus was four times wider here, than by RDRAM, they eventually coped with this task. NVIDIA nForce chipset for AMD processors was the first desktop chipset to feature two independent DDR SDRAM controllers. But it is systems based on Intel CPUs that feel most urgent need in dual-channel memory. The bus bandwidth of modern Pentium 4 processors is 4.2GB/s. The upcoming 800MHz bus is going to push the edge to 6.4GB/s. That’s why there have appeared several dual-channel Pentium 4 chipsets. Springdale and Canterwood chipsets from Intel are also going to occupy their place among the novelties of kind soon.

Not so long ago we reviewed the first dual-channel DDR chipset from Intel – Granite Bay or E7205. The well-known Pentium 4 chipsets maker, SiS, has offered an alternative aka SiS655. That’s what we are going to get busy with today.

Closer Look at SiS655

To cut a long story short, we have to say that SiS655 is a dual-channel reincarnation of another, quite successful product of the company: SiS648. Just have a look at the flow-chart of the new chipset:

We see that the features of SiS655 are absolutely the same as those found in SiS648, except the memory subsystem:

• Supports Intel Pentium 4 and Intel Celeron CPUs working with 400MHz and 533MHz bus;
• Supports AGP 3.0 specification. This means AGP 8x support and no backward compatibility with old 3.3V graphics cards.
• Improved MuTIOL bus connecting North and South Bridges of the chipset. Thanks to twice higher frequency (533MHz), its bandwidth is now 1.06GB/s.
• SiS963 South Bridge supports six USB 2.0 and three IEEE1394a ports, AC-97, MC-97, 10/100 Ethernet MAC and ATA 33/66/100/133.

The only specific thing about SiS655 worth mentioning is Hyper-Threading technology support. SiS’ website claims that SiS655 supports Hyper-Threading since revision B. By the way, the same thing is also valid for SiS648. However, you should understand that Hyper-Threading technology support doesn’t imply anything extraordinary. In order for the operation system to recognize two logical processors in a Pentium 4 3.06GHz, the system should send a command for the CPU to turn on this technology on start-up. The mainboard can issue this command, too, without any chipset intervention. So, if the mainboard’s BIOS supports two logical processors, you can go along without a Hyper-Threading supporting chipset. In other words, it means that mainboards based on SiS655 revision A can use Hyper-Threading, too. An example of such a mainboard is Gigabyte GA-8SQ800 Ultra, which we welcomed in our test lab. Although it was based on the first revision SiS655 chipset, the mainboard recognized both logical CPUs in one Pentium 4 3.06GHz.