SiS755: New Chipset for Athlon 64

by Ilya Gavrichenkov
12/16/2003 | 11:25 AM

When I started testing SiS755, a new chipset for Athlon 64 processors from Silicon Integrated Systems Corporation, a story of two years ago came to my mind. Back then, in the fall of 2001, chipset makers were only starting to produce chipsets with DDR SDRAM support intended for Socket A platform. AMD, VIA and ALi were the first companies to release such products. SiS was a little late then, but the tardy SiS735 turned to be the fastest Socket A chipset of that day, much to the surprise of the community. SiS showed the strength of the company’s engineering team, which managed to build the most efficient memory controller for DDR SDRAM. As a reaction to SiS’ success, other manufacturers were hastily releasing their products revisions with faster memory controllers.

This old story seems to repeat itself now. First of all, SiS is again a little late with a chipset for the AMD Athlon 64 platform since the mainboards on VIA K8T800 and NVIDIA nForce3 150 have long been in the market already, while analogous mainboards on chipsets from SiS are yet to arrive. On the other hand, the sales of the Athlon 64 processor itself have been low enough so far, so some delay won’t tell on the potential sales of the upcoming SiS chipsets. And they do come up along with SiS755-based mainboards. So, we decided it is high time we offered you a detailed coverage of the capabilities and performance of the SiS755 chipset. I am very excited to find out if SiS755 can repeat the success of the SiS735 predecessor. What surprises has SiS prepared for VIA and NVIDIA? Will it once again prove a manufacturer of high-performing chipsets?

SiS755: Closer Look

So, SiS755 is the first chipset from the series SiS is going to offer for the Athlon 64 processor family. Looking just at its formal specifications, SiS755 does not seem a jewel at all. I don’t mean to say that it lacks functionality; it is at the same level with other modern chipsets, but not any better than those. The specifications are actually quite ordinary according to the today’s standards.

As the flowchart suggests, the chipset consists of two chips: the SiS755 North Bridge and SiS964 South Bridge (although nothing prevents mainboard manufacturers from using other latest South Bridges from SiS as they are all pin-compatible).

SiS755 supports HyperTransport bus for communication with the processor with a bandwidth of 1.6GB/s. In other words, the bus is 16bit wide and works at 800MHz both ways. SiS755 is free from the drawback of the competing chipset from NVIDIA, nForce3 150, which has a cut-down version of the HyperTransport bus with a frequency of 600MHz and a width of 8bit one way.

SiS755 also contains the AGP 8x controller with Fast Writes support. An important note: the new chipset is also free from the drawback of the VIA K8T800 allowing more flexible control over the AGP (and PCI) divisors. It means we won’t have any problems with AGP and PCI devices when overclocking the CPU by boosting the FSB frequency. Moreover, like the NVIDIA nForce3 150, the new SiS chipset allows clocking the AGP/PCI frequencies asynchronously with those of the FSB. You can just lock the AGP frequency at its regular value. That’s truly the most important thing when you overclock the processor by raising the bus frequency.

Since the memory controller in Athlon 64 systems has been moved to the central processor, the life of chipset developers has now become much easier. The engineers don’t have to bother about creating efficient memory controllers, but can focus on the improvement of the AGP interface, the system bus and the bus linking the two chipset Bridges.

SiS755 uses an exclusive 16-bit bidirectional MuTIOL 1G bus to connect the North and South Bridges of the chipset. It has been long and successfully used in SiS products. The key feature of this bus is its multiple streams support. That is, any bandwidth consumer can be allotted some portion of the total bus bandwidth. The MuTIOL 1G can also portion the bandwidth to several independent streams simultaneously. The peak bandwidth of the MuTIOL 1G is limited at 1.07GB/s.

SiS964 South Bridge coming with the standard version of the SiS755 chipset is the most advanced chip SiS has at its disposal today. The chip supports all the necessary interfaces and protocols, including two ATA/133 channels and two Serial ATA-150 ports. SiS964 allows uniting the SerialATA drives into RAID arrays of levels 0 or 1 as well as arranging them into a JBOD array. SiS964 also supports eight USB 2.0 ports, PCI bus, 10/100Mbit LAN MAC, six-channel AC’97 sound and so on. In fact, SiS964 only lacks IEEE1394 (FireWire) support. Some of the older South Bridges from SiS do support this interface, so the company might have just considered it not worth including into the basic specification of SiS755 solution.

The table below compares the characteristics of SiS755 with the functionality of the already announced chipsets from VIA and NVIDIA intended for the Athlon 64 platform:

As we see, according to the formal specifications of SiS755, this solution looks much similar to VIA K8T800, save for the faster bus between the Bridges. Delving a little deeper, we may find some interesting things about SiS755, though. One of them is HyperStreaming architecture, which is a particular point of pride for SiS.

This architecture allows SiS to process the data streams inside the chipset North Bridge more efficiently. The architecture intellectually controls the data streams inside the chipset North Bridge, using advanced algorithms for conflicts arbitration. Processing a single stream, the architecture tries to minimize the latencies on the way. When there are several streams, special algorithms come into action to pipeline the transactions and perform them simultaneously. Besides that, the HyperStreaming architecture allows separating the streams into high-priority and ordinary ones, so some streams can get a reserved bandwidth portion for their needs.

Unfortunately, I cannot claim that this architecture is unique nowadays, since I don’t know what technologies VIA and NVIDIA use in their chipsets. Anyway, the tests you are going to see shortly prove that SiS755 does handle data more efficiently than the competitor products.

SiS755 Based Reference Board: Closer Look

We tested the performance and features of SiS755 using a reference board from SiS based on it. Now I would like to say a few words about the board, of course:

Once again, the PCB design of SiS755 based reference board is the same as that of the SiS760 based one, so these two chipsets are truly pin-compatible. As you can see, the mainboard has a landing-place for the memory of the local frame buffer. I do hope we will be able to test SiS760 soon, too.

I don’t think it really makes much sense to dwell for long on the reference design of the SiS755 based board as this mainboard has nothing to do with the actual products. So, I will just show you a few snapshots:

SiS755 North Bridge

SiS964 South Bridge

Mainboard rear panel.

Note the six USB 2.0 ports at the back panel of the board. We also have non-operational TV-out and D-Sub connectors here, as SiS755 doesn’t include an integrated graphics core.

A small passive heatsink is mounted on top of the chipset; the local frame-buffer should occupy the neighboring spots.

Testbed and Methods

The point of our today’s testing is to check the performance level of the new SiS755 chipset compared to the competitor products. Some time ago, we tested thirteen mainboards on NVIDIA nForce3 150 and VIA K8T800 chipsets (see our Socket754 Platform: 13 Mainboards Roundup for details), so it was an easy one to choose a rival for the SiS755 reference board. The only factor to limit out choice was the fact that the reference board from SiS had slightly overclocked processor bus (by about 1%):

So, we took a Chaintech ZNF3-150 (NVIDIA nForce3 150) and a Gigabyte GA-K8VT800 (VIA K8T800) that also have a slightly overclocked FSB. Moreover, according to our tests, these two mainboards are among the fastest products on the corresponding chipsets. The testbed we used to test SiS755 looked as follows:

• AMD Athlon 64 3200+ CPU (2.0GHz);
• Chaintech ZNF3-150 and Gigabyte GA-K8VT800 mainboards, and SiS755 reference board;
• 512MB DDR400 SDRAM (2-2-2-6 timings);
• NVIDIA GeForce FX 5900 Ultra graphics card (Detonator 52.16 driver);
• Western Digital WD400JB HDD.

We ran the tests in Windows XP Professional SP1 with DirectX 9.0b installed. We also used the following chipset drivers: NVIDIA nForce3 Unified Driver 2.65, VIA Hyperion 4-in-1 Driver v.4.49 and SiS AGP Driver 1.17a.

Performance

When writing a chipset review, I used to test the performance of the memory subsystem first, but this tradition has come to an end. In Athlon 64 platforms the memory controller is inside the processor, and its performance doesn’t practically depend on the design of the chipset or mainboard, so any mainboards on any chipsets will show similar speed in memory performance tests. So, what should the chipset maker be concerned about to optimize the performance of its Athlon 64 chipset? I think it is primarily the efficiency of the controllers of the HyperTransport and AGP busses as well as fast work of the subsystems grouped in the South Bridge.

So, we are mostly interested in gaming tests. The benchmarks of this type load both: HyperTransport and AGP buses to reveal the weak and strong points of each chipset considered.

The CPU test from the 3DMark03 suite doesn’t reveal any difference between the chipsets. Well, it shouldn’t, actually. This rating mostly depends on CPU and memory subsystem speeds, so it just barely touches the chipset itself.

The 3DMark03 test can put every subsystem under serious workload. We see different chipsets providing different performance. The HyperStreaming architecture of SiS755 shows its best here, so that the SiS product becomes the leader.

These relatively old games are easily digested by a modern system, and the use of different chipsets affects the overall result really slightly. Moreover, SiS755 even manages to fall behind the others in Quake 3: Arena for some mysterious reason.

Modern DirectX 9 games operate with huge data amounts and pinpoint any weakness of the platform they run on. We told you in our Socket754 mainboards roundup that these two games emphasized the main disadvantage of the NVIDIA nForce3 150: its slower HyperTransport bus. Today, X2 – The Threat shows the advantage of the HyperStreaming architecture, while Tomb Raider: The Angel of Darkness proves that the HyperTransport bus in SiS755 works just fine.

The next bunch of tests includes office and content-creation applications from the Winstone benchmarking package.

Different chipsets behave very similar to one another in these tests. It means SiS755 comes with a well-designed IDE controller, which plays the crucial part in the results of the Winstone tests. However, I should acknowledge that the nForce3 150 is still somewhat faster here.

SiS755 is wrestling with NVIDIA nForce3 150 in the encoding tasks. It wins the first round (Windows Media Encoder 9), but loses the other two.

We used the CINEMA4D package to check out the performance of the mainboards in professional OpenGL applications. As you can see from the diagram, SiS755 is the best here.

Conclusion

Silicon Integrated Systems came to the market of Athlon 64 chipsets later than the others, but with a really worthy product. SiS755 chipset offers the full range of modern functions and excellent performance. SiS755 based reference board was faster than off-the-shelf mainboards on the VIA K8T800 and NVIDIA nForce3 150 across a majority of tests. When SiS755-based mainboards appear in shops, they are sure to become a highly demanded product.

SiS again upholds its reputation of a strong player in the chipset market. The company’s exclusive HyperStreaming architecture yields dividends in the way of increased performance. SiS755 is also free from the shortcomings of the competitor products. It has a full-speed HyperTransport bus, unlike NVIDIA nForce3 150, and it allows locking the AGP/PCI frequency, contrary to VIA K8T800. The latter fact may ensure good overclockability of SiS755-based mainboards. Well, as for overclocking, we should better wait for the mass mainboards to arrive and see what they can offer us in this respect.

Anyway, I can claim that SiS755 is the best chipset for the Athlon 64 platform today. It’s only and biggest drawback is that there are no mainboards based on it in the market yet. By the time they do make it into the market, the situation may change. NVIDIA is planning to release their improved Athlon 64 chipset, NVIDIA nForce3 250, while VIA is busy polishing off the K8T800. So, I only hope we will see products on SiS755 soon enough.