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

by Ilya Gavrichenkov
03/21/2003 | 01:49 AM

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.

Now let’s talk about the main innovation of SiS655: new memory subsystem supporting two DDR SDRAM channels. The chipset’s dual-channel memory subsystem officially supports DDR266 and DDR333 SDRAM thus providing up to 5.4GB/s bandwidth. It’s even more than modern Pentium 4 processors can use up. Moreover, SiS655 delivers the highest memory bandwidth among all currently available chipsets for Socket 478 processors.

Note also that although the official SiS655 specs tell only about DDR266 and DDR333 support, the real capabilities of the chipset are much wider. Of course, we have DDR400 SDRAM support here: it was unofficially implemented in SiS645DX already. Moreover, the numerous possible values of the memory bus devisor allow setting memory frequency with the same flexibility as in NVIDIA nForce2 based systems.

The chart shows there are two independent memory controllers in SiS655 with their own address, data buses and so on. In other words, SiS engineers used the same approach as NVIDIA did in its nForce2 solution for Athlon XP platforms. This allows flexible configuration of the memory subsystem and the use of different-type DIMM pairs. SiS went even farther: SiS655 can work in three memory access modes chosen according to the configuration and number of installed modules and according to user’s settings, of course. Let’s describe each mode.

The simplest work mode implies single-channel 64-bit memory access. This mode is activated when there is only one memory module in the system, or two modules are installed into slots referring to one and the same channel. In this case, only one controller of the two is in use, the other one remains idle. So, the chipset works as a traditional single-channel chipset in this mode.

The second mode provides dual-channel 64-bit access. It can be used when you install modules into DDR DIMM slots referring to both controllers. As the controllers of SiS655 are fully independent, the modules assigned to each channel may differ in capacity, quantity and organization.

The third, single-channel 128-bit mode “couples” the controllers to work with the memory as if there were a 128-bit bus. This mode requires that the memory modules in both channels are installed in pairs and are absolutely identical.

SiS claims the memory subsystem performs about the same in 128-bit and dual-channel 64-bit modes. Meanwhile, our tests show that 128-bit mode allows getting a bit higher effective bandwidth, while dual-channel 64-bit mode allows getting lower latency of the memory subsystem.

Overall, SiS655 is one of the most advanced chipsets today. Only the upcoming chipsets from Intel with 800MHz bus support will probably push the performance edge further ahead. But, they are to come only 2 months later…

SiS655 against Intel Chipsets: Specification Comparison

To confirm our words, we present a table listing specifications of SiS655 and contemporary chipsets from Intel. It shows that SiS655 offers richer capabilities than analogous Intel products.

Well, we think the advantages of SiS655 are evident. At the same time, SiS655 is no match for Intel E7205 in the server market. First of all, it can’t elbow its way into the High-End because of the “non-aristocratic” origin and secondly, it lacks ECC support.

Closer Look at Gigabyte GA-8SQ800 Ultra Mainboard

Gigabyte is actively expanding its market presence and is one of the first to roll out mainboards based on new chipsets. Gigabyte GA-8SQ800 Ultra is an excellent example. That’s why we decided to get acquainted with SiS655 with the help of this product.

SiS655 represents an alternative to a more expensive Intel E7205 in the desktop market. Therefore, Gigabyte did its best to implement as many extra features as possible, so that they could position this product as a solution for high-performance systems of enthusiastic PC users.

Notwithstanding all the integrated stuff, the design of Gigabyte GA-8SQ800 Ultra can be considered a success. The mainboard carries an AGP 8x slot equipped with a fastening latch, five PCI slots and four DDR DIMM slots (two for each of the memory controllers). The design layout is handy; there should be no problems during installation. Our only critical remark to Gigabyte’s product concerns the connection of the riser-card. This card provides three IEEE1394 ports supported by the controller integrated into the chipset South Bridge. When installed, it hangs above the PCI slot located next to the AGP, so that you appear unable to use it. As a result, the cooling of the graphics card may be hindered. Moreover, GeForceFX owners would have to give up IEEE1394 ports as the cooling system of this particular graphics card takes up the room above the neighboring PCI slot completely.

Thanks to the South Bridge, the mainboard supports six USB 2.0 ports. A back panel bracket coming with the mainboard carries four of them.

Integrated controllers also add a lot to mainboard’s functionality. Gigabyte GA-8SQ800 Ultra features an ordinary Fast Ethernet chip from Realtek and a six-channel AC’97 ALC650 controller with SPDIF output support. Among more exotic capabilities we can name SerialATA RAID and ParallelATA RAID controllers. SerialATA RAID is provided by Sil3112A chip from Silicon Image supporting two channels and arrays of level 0 and 1. GigaRAID ITE IT8212F chip provides Parallel ATA RAID. GA-8SQ800 Ultra is the first mainboard where we meet this chip. It supports two ATA-133 channels and arrays of level 0, 1 and 0+1.

Besides, Gigabyte has also implemented one more innovation in its GA-8SQ800 Ultra mainboard, which has to do with easy connection of HDDs. For this purpose they included a special GC-SATA bracket into the mainboard package. This panel allows placing the Serial ATA connectors implemented via the Silicon Image controller at the back panel of the PC case. In other words, with a GA-8SQ800 Ultra mainboard and GC-SATA bracket you may get the opportunity to connect your SerialATA hard disk drives to your computer as external ones. Moreover, in this case not only SerialATA connectors will be moved to the back panel, but also the necessary power connectors for the HDDs. Inside the chassis, the GC-SATA is connected to the onboard SerialATA connectors and to the power supply unit.

One more house technology from Gigabyte is Dual BIOS. There are two flash-memory chips on the mainboard PCB that store two copies of the system BIOS. A special utility integrated into the BIOS code helps to copy the data between the chips and also boot up from either of them. As a result, an accidental damage of the flash-memory data (for example, after an incorrect BIOS update) won’t be a problem.

As for overclocking, Gigabyte offers a dainty bit here. First, we were simply impressed but the widest FSB frequency range available in BIOS we have ever seen: from 100 to 355MHz. You can argue about the necessity of this sky-high upper value, but Gigabyte claims that GA-8SQ800 Ultra will support the upcoming CPUs with 800MHz bus. The mainboard also allows adjusting three voltages: Vcore, Vdimm and Vagp. CPU voltage may be set to any value from 1.55V to 1.85V with 0.025V increment; DIMM voltage can be set to 2.5V or 2.6V; AGP voltage – to 1.5V or 1.6V. The AGP/PCI frequency can be changed independently of the FSB frequency. Besides that, the BIOS Setup of GA-8SQ800 Ultra offers options for basic memory timings adjustment and setting the dual-channel mode for the memory controllers. But these options are hidden by default. In order to reach this sub-menu of BIOS Setup, press Ctrl + F1.

Despite all the indisputable advantages, the overclocking friendly features set of GA-8SQ800 Ultra lacks one important thing. The mainboard doesn’t allow re-setting CPU and memory parameters in case of “over-overclocking”. Moreover, there is no Clear CMOS jumper – a useful tool for every overclocker.

Testbed and Methods

The goal of the today’s review is to reveal the performance level of the new dual-channel DDR SDRAM chipset from SiS – SiS655. We will compare it with modern chipsets from Intel: E7025, i850E and i845PE. All the participating chipsets were benchmarked in all possible work modes with a Pentium 4 3.06GHz CPU (Hyper-Threading was activated).

We tested SiS655 in three work modes: single-channel 64-bit, single-channel 128-bit and dual-channel 64-bit memory access modes. The memory clock-rate was set at 266, 333 and 400MHz. Intel chipsets were also tested in all available work modes.

As a result, our testbeds were configured as follows:

All the benchmarks were run in Microsoft Windows XP Professional. The mainboards were set to maximum performance by means of setting the lowest possible timings our memory modules allowed (2-2-2-5 at 266MHz memory frequency, 2-2-2-6 at 333MHz memory frequency and 2-3-3-7 at 400MHz memory frequency). By the way, we used high-quality Corsair XMS3200 DDR SDRAM.

Performance

First of all, let’s run the synthetic Cachemem benchmark to test memory controllers of the reviewed chipsets.

Let’s analyze the results. First of all, SiS655 certainly justifies our hopes and shows high performance with the memory. Thus, this chipset with dual-channel DDR333 and DDR400 outperforms i850 with dual-channel RDRAM as well as single-channel i845PE. In fact, there is only one worthy rival – Intel E7205. Although Intel’s chipset uses slower DDR266 memory, lower latency helps it to show high results. We should also keep in mind that the peak bandwidth of the Pentium 4 bus is 4.2GB/s, which exactly corresponds to the throughput of dual-channel DDR266.

Meanwhile, we should note that the use SiS655 in dual-channel mode with fast memory types, like DDR333 and DDR400, will allow increasing the write and copy speeds as well as lower the memory latency.

Comparing the results of SiS655 with DDR400 and DDR333, we see that nominally faster DDR400 is greatly hindered by its high latency. It means that SiS655 might be faster with DDR333 in many applications. Moreover, SiS optimized its chipset exactly for this memory type.

There is also a perceptible difference between the two dual-channel modes of SiS655. 128-bit memory access provides higher effective bandwidth, while 64-bit mode – lower latency. So, we may suppose SiS655 would show its maximum performance in 64-bit dual-channel DDR333 SDRAM mode. We will see it in real applications later in the article.

Now let’s turn to another memory bandwidth test aka, SiSoft Sandra 2003, which uses the well-known Stream algorithm.

SiSoft Sandra indicates that SiS655 with dual-channel DDR333 and DDR400 SDRAM is the best of all. We should note, however, that the peak effective bandwidth of such high-speed memory (its theoretical bandwidth is 5.4 or even 6.4GB/s) can’t reach the theoretical maximum of the CPU bus – 4.2GB/s. This suggests that we shouldn’t expect any considerable performance growth over the dual-channel DDR266 platforms.

But let’s go over from synthetic benchmarks to real applications.

This benchmark is based on business applications (including Lotus Notes R5, Microsoft FrontPage 2002 SP-1, Microsoft PowerPoint 2002 SP-1, Microsoft Excel 2002 SP-1, Microsoft Access 2002 SP-1, Microsoft Word 2002 SP-1, Microsoft Project 2000, WinZip 8.0, Norton AntiVirus from Symantec and Netscape 6.2.1). SiS655 shows excellent performance here – better than all the competitors from Intel.

We have similar results in multimedia applications (Multimedia Content Creation Winstone 2003 includes Adobe Photoshop 7.0, Adobe Premiere 6.0, Macromedia Director 8.5.1, Macromedia Dreamweaver 4, Microsoft Windows Media Encoder 7.01.00.3055, Netscape 6.2.3, NewTek LightWave 7.5 and Sonic Foundry Sound Forge 6.0). We can only be pleased with SiS. Every new chipset from the company is better than the previous products and competes on equal terms with Intel chipsets.

Dual-channel PC1066 RDRAM i850 was best at zipping files with WinRAR. SiS655 does quite well, too, and outperforms Intel E7205.

Video encoding into MPEG-4 format shows similar picture.

The half-synthetic PCMark2002 once again brings SiS655 to the fore. Due to a combination of high bandwidth and relatively low latency outpaces all its competitors.

Next we tested SiS655 in gaming benchmarks. First we used 3DMark2003, which shows performance of the platforms in 3D games of tomorrow.

SiS655 with DDR400 and DDR333 SDRAM, Intel E7205 and i850 show similar results in this test. If we exclude the graphics subsystem workload and have a “pure” mainboard performance, we will have the following picture:

The ratings in the diagram are calculated by benchmarking the system at software vertex processing. As we see, SiS655 is far from best here. The first place goes to i850 working with PC1066 RDRAM.

Seems like i850E remains the best choice for game platforms. It won Return to Castle Wolfenstein. Still, SiS655 is faster here than any DDR SDRAM chipset from Intel.

Intel chipsets win Unreal Tournament, too. And here both Intel E7205 and i850 prove very strong.

Then, we tested the chipsets in SPECviewperf 7.0. It measures the system performance in typical professional OpenGL applications. These benchmarks suit well for comparison of different chipsets, as their results are greatly dependant on effective CPU-memory communication.

In this class of applications (professional OpenGL), SiS655 shows rather average performance. So, the new SiS chipset is not the one to be used in workstations, the solutions from Intel will might a better choice in this case.

Conclusion

Once again SiS launches a successful product for Pentium 4 platform. From this point of view, SiS655 is a worthy successor to SiS648 and SiS645DX. Combining a rich feature set, Hyper-Threading support and dual-channel memory access mode, SiS655 can outperform chipsets from Intel in a number of applications. On the other hand, there are still things to be improved. SiS655 was slower than expected in modern games and professional OpenGL applications.

Anyway, the strongest point of chipsets from SiS has always been an affordable price. Now, you can count out about $200 and buy an E7025 based mainboard, or you can purchase an analogous SiS655 based product for about $140.

We should also remind you that SiS655 might have a short lifecycle. Intel is going to use its new CPUs with the 800MHz bus and it’s still not clear about the support of this bus in SiS655. Anyway, if you are choosing a Pentium 4 platform today, we advise you thoroughly consider SiS655.