SiS, which already managed to surprise us several times, has finally defined its top priority in the chipset business. Despite the fact that SiS managed to release a few very successful products for both: Athlon and Pentium 4 systems, since they had returned to the discrete chipset market, they are now going to focus mostly on solution for Intel platforms.

It was first of the current market situation that stimulated this decision. In the Pentium 4 sector SiS seems to have only one worthy competitor now: Intel. ALi hasn't yet managed to start shipping its Pentium 4 chipsets in mass quantities and VIA doesn't have Intel's license, and NVIDIA is not into this market at all. This way SiS has the whole lot of opportunities ahead. However, in the market sector for Socket A processors, SiS faces much more violent competition. Moreover, SiS hasn't been very successful lately with the chipsets for AMD CPUs, to tell the truth.

As for the Pentium 4 solutions, SiS will do its best to reach the top of 30% market share by the end of H1 2002. And the major weapon SiS is going to use in this battle for the sacred 30% is the same as it used to be: the company will do its best to implement new technologies ahead of Intel this way winning the hearts of new mainboard manufacturers.

The first Pentium 4 chipset from SiS, SiS645, launched in the end of last year, allowed building DDR systems with Pentium 4 before the DDR version of i845 came out. Moreover, SiS645 featured the revolutionary support of DDR333 memory, which made it nearly as fast as i850, which still remains the fastest Pentium 4 core logic.

And again SiS resorts to an old trick. On March 13 the company announced its new Pentium 4 core logic aka SiS645DX, which appeared the first solution supporting Pentium 4 processors with 5333MHz Quad Pumped Bus. Intel is planning to release its own solutions withy similar features a bit later, in May, together with the corresponding CPUs. However, though there are no processors supporting new 533MHz bus, SiS645DX looks very attractive due to its huge potential for further upgrades.

Well, we can't help taking a closer look at one more interesting solution for Pentium 4 platform. So, here we go!

Closer Look: SiS645DX Chipset

I would like to draw your attention to the fact that even the names of SiS645DX and its predecessor differ a very tiny bit, which indicates high level of similarity between the chipsets. Firstly, SiS645DX features a new North Bridge adding the official support of 533MHz Quad Pumped Bus to SiS645. And secondly, this chipset comprises the new revision of SiS961 South Bridge - SiS961B, which boasts ATA/133 protocol support used by new Maxtor drives, by the way. And that's it: there are no other innovations in the SiS645DX solution.

This way you can get a pretty good idea about SiS645DX from our previous SiS645 Chipset Review and from the recent article called Contemporary Pentium 4 Chipsets Comparison. I would only like to stress that SiS645DX is built on a new A2 revision of SiS645 with an enhanced memory controller.

Moreover, as we have already mentioned in our review called Three SiS645 Based Mainboards: ASUS, MSI and ECS, even SiS645 already supported 533MHz processor bus, though unofficially, of course. All mainboards based on it allowed setting the FSB frequency to 133MHz, while the AGP and PCI bus frequencies remained equal to the nominal, and the stability of the entire SiS645 based system didn't arouse any complaints.

Therefore, we get the impression that there are hardly any changes in the new SiS645DX North Bridge. And the only thing SiS did to launch a new chipset revision were the stability tests proving that 133MHz FSB can be set safely.

   

However, in reality the changes in the SiS645DX chipset North Bridge appear pretty significant. Just like in case of SiS645 when it turned out capable of supporting 533MHz bus, SiS645DX boasts undeclared ability to work not only with DDR266 and DDR333 memory but also with DDR400 SDRAM. To prove this point I would like to let you see two pics of the ASUS P4S533 (SiS645DX) mainboard BIOS Setup. These pictures show clearly that when the FSB frequency is set to 100MHz and 133MHz the memory bus can be clocked for 400MHz (200MHz DDR).

Although SiS645DX works quite OK with the DDR400 memory, SiS decided not to include the support of this memory type into the official specs sheet for SiS645DX. The reason is probably connected with the currently indefinite status of DDR400 memory. Although Micron and Samsung do have the DDR SDRAM samples working at 400MHz already, JEDEC haven't yet arrived at any conclusion about the vital capacity of 400MHz DDR I. Therefore, DDR400 SDRAM is not selling yet.

At the same time, the use of DDR400 in Pentium 4 systems may bring in significant profits. Let's have a look at the peak theoretical bandwidths of the memory types used in today's Pentium 4 systems:

As you may notice, the bandwidth of DDR400 makes 3.2GB/sec, which is about the same as provided by dual-channel PC800 RDRAM used in i850 based systems. Bearing in mind that i850 has been the fastest Pentium 4 chipset up to nowadays and DDR SDRAM boasts lower latency than RDRAM, we can conclude that a solution working with DDR400 will undoubtedly become a new performance leader among the Pentium 4 chipsets. Only the future i850E based systems built with PC1066 RDRAM could compete with DDR400 platforms (i850E is due on May 6). Later in this article we will discuss the performance advantages provided by DDR400 with SiS645DX, so go on reading :)

SiS645DX and Its Competitors

As usual, I would like to sum up all the specifications for the currently available Pentium 4 chipsets in a single table:

Even a quick glance is enough to understand that SiS645DX boasts the most attractive feature of all today's Pentium 4 chipsets. However, you should bear in mind that the main competitors are to come in May. In the beginning of the month we will see i850E supporting RDRAM memory, and differing from the predecessor by the support of faster 533MHz Quad Pumped Bus, PC1066 RDRAM and USB 2.0. In the end of May we should witness the birth of Intel's DDR solution, i845E, also supporting 533MHz bus and USB 2.0. The recently launched VIA P4X333 chipset is expected to start shipping in mass in May as well. This solution boasts more advanced features and supports not only 533MHz bus, but also DDR333 memory, AGP 8x, 533MB/sec V-Link bus and USB 2.0.

As a result, SiS645DX will no longer look as winsome, as it does now. However, we all should understand that SiS645DX will not stay in the market for long. In May SiS will launch their new SiS648 solution supporting AGP 8x, USB 2.0 and IEEE 1394, and a bit later its enhanced SiS648DX version officially supporting DDR400. In general, the end of spring promises to be really hot for the Pentium 4 chipset market.

Well, before we pass over to the benchmarks, let's take a closer look at SiS645DX based mainboard we had at our disposal.

Closer Look: ASUS P4S533 Mainboard

We got our hands on the first mass mainboard based on SiS645DX. Strange as it might seem, but this was not a product from ECS, which used to be the first to manufacture SiS based mainboards, but from another well-known company: ASUS. The mainboard manufacturers have been very concerned lately about the too close cooperation between SiS and ECS, which implied that ECS received the chipsets from SiS much earlier than everyone else. Besides, the prices for ECS were a lot lower than the official ones. As a result, SiS had to correct its strategy and now there are no longer so many privileges for ECS. This is one of the reasons why ASUS and not ECS appeared the first to start shipping mass mainboards based on SiS645DX. All in all, ASUS started paying more attention to SiS chipsets lately, which is reflected by its today's product range.

So, let's have a look at ASUS P4S533 mainboard:

ASUS P4S533
Supported CPUs	Socket478 Intel Pentium 4
Chipset	SiS645DX (SiS645DX + SiS961B)
FSB Frequencies	100-166MHz
Overclocking Friendly Features	Supports Vcore and Vmem Adjustment
Memory	3 DIMM slots for DDR200/DDR266/DDR333 SDRAM
Expansion Slots (AGP/PCI/ISA/CNR)	1/6/0/0
USB 1.1 Ports	6
USB 2.0 Ports	0
IEEE 1394 Ports	0
Integrated Graphics	No
ATA-100/133 support	+/+
Integrated Sound	6-channel controller from C-media - CMI8738
Integrated LAN	Integrated controller from Realtek
Additional Features	ASUS Q-Fan technology, Smart Card/MS/SD support, voiced diagnostics system
BIOS	Award Medallion BIOS v6.00
Form-Factor	ATX, 305x222mm

The specs and picture of ASUS P4S533 mainboard shows that this solution is very similar to another ASUS mainboard on SiS645 chipset: P4S333 (see our article called Three SiS645 Based Mainboards: ASUS, MSI and ECS). It's true: P4S533 is very similar to the predecessor's PCB, so that many features and peculiarities are the same in both cases. However, these two mainboards are no twins, and there are some differences between them worth mentioning.

First of all, I would like to say that even though P4S522 is none other but the next version of P4S333, their PCBs are not fully identical. First of all, P4S533 has no ACR slot, which we saw on P4S333. So, our today's hero features 6 PCI and an AGP 4x slot.

Secondly, the hardware monitoring scheme has also been changed a bit. Unlike its predecessor, ASUS P4S533 started supporting Q-Fan technology, which implies that the CPU cooler fan rotation speed varies depending on the CPU temperature. In reality it means that when the CPU temperature drops below 50 degrees Centigrade, the fan connector receives lower voltage, which in its turn reduces the noise level noticeably.

I would also like to point out that ASUS will position its P4S533 mainboard as a low-cost Pentium 4 solution. That is why the manufacturer didn't pack it with the whole lot of external controllers, having added only a 6-channel C-Media CMI8738 sound controller, Realtek network controller and Smart Card Reader support alongside with Secure Digital and Memory Stick card readers.

Since the PCB is not very complex, it is of relatively small size and the design is quite convenient: all connectors are easy to reach. The only thing we could point out to ASUS' engineers is the location of the AGP slot, as the graphics card installed into it locks the DIMM clips completely. As for the design peculiarities, we could mention the processors socket turned by 90 degrees relative to the common location. Although, this location of Socket478 doesn't have any negative influence.

P4S533 doesn't require new PSUs with an additional 12V cable, which comply with ATX 2.03 specifications. It works quite fine with the regular power supply units, but for greater stability it is equipped with a connector for 12V cable, just like the one used for HDDs. However, as our tests showed, it can work fine without any 12V power supply at all.

Just like all ASUS products, ASUS P4S533 supports voiced diagnostics system based on W83791SD from Winbond.

The BIOS of our mainboard is based on Award Medallion BIOS and features all the setting for detailed memory configuring. The mainboard allows setting the CPU and memory bus frequencies as 1:1, 3:4, 3:5 and 3:6 when the FSB frequency is equal to 100MHz, or as 1:1, 4:3, 4:5 and 4:6 when the FSB frequency is set to 133MHz. Also you can set CAS Latency, RAS to CAS Delay, RAS Precharge Time, RAS Active Time, SDRAM Command Leadoff Time and Optimization mode to Turbo, Fast or Normal.

As for overclocking, BIOS offers the whole bunch of functions for that. The FSB frequency can be adjusted in the interval from 100MHz to 166MHz with 1MHz increment. In case the FSB frequency falls between 100MHz and 132MHz, the PCI frequency is obtained from the FSB frequency as 1:3; and starting from 133MHz FSB, the ratio gets equal to 1:4. The processor Vcore can be increased by 0.2V with 0.025V increment. Vdimm can be also increased from 2.5V to 2.7V or 2.9V with a special jumper in the lower right corner of the PCB.

This mainboard proved pretty stable during the tests with DDR333 and DDR400 memory, however, I wouldn't call it impeccably stable when working with DDR266. In fact, I believe that they will eliminate this problem in the future BIOS updates (we used BIOS version 1006 with our mainboard).

Testbed and Methods

Since the performance of SiS645DX working with CPUs with 400MHz bus should theoretically coincide with that of SiS645 Rev.A2, which we have already tested (see this review), we has to veer a bit away from the standard testing algorithm. For instance, we didn't compare the performance of SiS645DX with that shown by the predecessors. We simply compared its fastness when working with DDR266 and DDR333 memory with that shown by the other latest Pentium 4 solutions, such as i850, i845 and VIA P4X266A.

Moreover, we were very much interested in checking how fast it is when working with DDR400 memory. Especially, since SiS645DX gave us a perfect opportunity to do it. That is why the diagrams also contain the results for SiS645DX+DDR400, even though this combination is not supported officially.

I would also like to say a few words about the DDR400 memory we used in our tests. As none of the system memory makers announced the beginning of DDR400 modules mass shipments, they are unavailable in the market. However, it turned out that high-quality DDR333 memory modules can be easily overclocked up to 400MHz. For example the PC2700 CL2 DDR SDRAM module from Twinmos based on Samsung chips worked stably at 400MHz. Though we had to set CASE Latency at 2.5.

All the test we have just described were run with Pentium 4 2.2GHz CPU with 400MHz bus, since the processors with 533MHz bus haven't been announced officially yet.

This way, we assembled the following testbeds:

All benchmarks were run in MS Windows XP Professional.

Since SiS645DX also supports Pentium 4 processors with 533MHz bus, we tested a system built with ASUS P4S533 with Pentium 4 (Northwood) 1.6AGHz overclocked to 533MHz bus frequency. This way its actual frequency in these systems made 2.133GHz. In this case we didn't compare the performance of SiS645DX based system with that of any other chipsets, since there are no other solutions in the market officially supporting processors with the bus frequency like that.

Performance

First of all, I would like to advise once again that you read our recent Contemporary Pentium 4 Chipsets Comparison, because today we will not return to some basic things discussed in that article in great detail.

As usual, we will start our test session with SiSoft Sandra benchmark measuring the peak memory bandwidth of different chipsets.

Please, look at the results shown by SiS645DX with DDR400 memory. They are even higher than the practical bandwidth of i850! However, there is nothing to be so greatly surprised at: the bandwidth of DDR400 SDRAM and dual-channel PC800 RDRAM used in i850 based systems is similar, while the latency is lower by DDR memory, of course. Therefore, SiS645DX has every chance to become the fastest core logic for Pentium 4 systems when combined with DDR400 memory. At least until the launching of i850E, which will support even faster dual-channel PC1066 RDRAM.

Frankly speaking, SYSmark is a relatively bad test for chipsets. The results shown by all chipsets are almost similar. Nevertheless, the results of SiS645DX with DDR400 as well as with DDR333 are a little bit higher than those demonstrated by other chipsets.

The same thing is valid for the performance in mp3 encoding benchmark.

The fastness of video encoding into DivX MPEG-4 format depends much more on the memory subsystem performance. That is why SiS645DX with DDr400 memory is considerably faster than all other chipsets, including i850 suffering from high latency of the memory subsystem.

In 3DMark2001 SE the former leader, i850, appeared destroyed by the newcomer with DDR400 memory.

Here the situation is similar to the previous case. Though i850 used to beat all other DDR chipsets in 3D games, the use of DDR400 memory let SiS645DX oust the competitor from the leader's pedestal. The remarkable thing is that SiS645DX is 4.5% faster than i850, which is a real lot, we should say.

In Serious Sam: Second Encounter the SiS chipset performs pretty well no matter what memory is used.

Here the picture is similar to what we saw in Quake3 Arena. SiS645DX with DDR400 outpaces i850, which used to be an indisputable leader here as well.

The results of the professional SPECviewperf benchmark are hardly any different from what we saw in 3D games. DDR400 again helps SiS645DX lead the race.

In Viewports of 3ds max 4.26 the things are just the same as in the previous tests.

PCMark2002 synthetic benchmark shows similar results. However, according to the numbers we obtained, the memory subsystem of SiS645DX appears faster than that of i850 with DDR333 already.

Now let's pass over to some benchmarks, which we ran with a CPU featuring faster 533Mhz bus. For these tests we used an overclocked Pentium 4 1.6AGHz CPU. So, in our system it worked at 2.133GHz core clock. Since SiS645DX is now the only chipset in the market officially supporting 533Mhz bus, we simply compared the performance of configurations built with SiS645DX based mainboard and DDR226, DDR333 and DDR400 memory.

The increase in the CPU bus frequency leads to the increase in its bandwidth up to 4.3GB/sec. It means that the memory bus in these systems will be used much more intensely. Especially, since the bandwidth of DDR400 turns out lower than the processor bus bandwidth in this case. As a result, we see that the practical memory bandwidth measured by SiSoft Sandra makes 98% of the theoretical bandwidth for DDR266, 93% of the theoretical bandwidth for DDR333 and 91% of the theoretical bandwidth for DDD400. As you see, the memory is used in a much more efficient way here, as in case of a CPU with 400MHz processor bus these numbers turn out equal to 98%, 85% and 80% respectively.

As a result, the performance difference between the systems with various memory types used increases.

Conclusion

In fact, the SiS645DX chipset itself didn't bring in any revolutionary innovations. It is analogous to SiS645 supporting 533MHz processor bus. That is why it will look attractive only until the launching of solutions with similar feature from other manufacturers. Therefore, SiS considers its SiS645DX only as a transitional product, which should let the company stress its technological leadership while the more advanced SiS648 is not there.

However, SiS645DX has one very cool undocumented feature. This chipset unofficially supports DDR400 SDRAM. This is exactly the peculiarity that shows this solution from a totally different view angle. Since the bandwidth of DDR400 makes 3.2GB/sec (the same as by 400MHz Pentium 4 bus or dual-channel PC800 RDRAM), SiS works performance wonders with this memory type. As our tests showed, SiS645DX with DDR400 is an indisputable leader today. There is only one upsetting thing about this victory: DDR400 memory modules are not available in stores yet. That is why you will have to look for high-quality well overclockable DDR333 if you decide to build a system like that.

But even if you don't use the cool DDR400 memory, the price-to-performance ratio offered by SiS645DX still looks very attractive. This is a really low-cost solution supporting DDR333 and leaving room for further upgrade once Pentium 4 processors with 533MHz bus are out. All in all, SiS645DX boasts all the advantages inherited from SiS645.

As for the mainboard we reviewed, ASUS P4S533, which is the first mass product based on SiS645DX, it represents a perfect implementation of the features offered by SiS' chipset. If you like SiS chipsets (and there is every reason for that, believe me), then ASUS P4S533 may turn out a perfect choice to make.