Summary: With its 533MHz bus, DDR400 memory support, and AGP 8X interface, the SiS 648 certainly offers a compelling feature set for the Pentium 4 platform. When you throw in the inexpensive price we're expecting most motherboards to go for, SiS 648 becomes even more compelling. But is it fast enough the dethrone an 850E system equipped with 1066MHz RDRAM? Find out in our preview of this upcoming chipset!
From zero to hero
While Silicon Integrated Systems (SiS) may not be a household name just yet, no other chipset manufacturer has been on as an incredible roll as the Taiwanese chip manufacturer. Just over a year ago SiS was a tiny player in the desktop chipset market, competing heavily with Acer Laboratories for that coveted third spot between industry veterans Intel and VIA Technologies. Rather than focusing on the desktop, SiSí primary hopes lied in its chipsets for the mobile market. With an expensive, delayed, 0.18-micron fabrication facility just coming online, many industry analysts wondered how SiS planned to grow its business, much less continue to exist at all.
The SiS 648 chipset is composed of the SiS 648 North Bridge (which connects the chipset to the CPU, graphics card, and system memory) and the SiS 963 South Bridge (which supports system peripherals such as the keyboard and mouse, and contains the hard drive and USB controllers among other items). If a motherboard manufacturer desires, the SiS 963 chip can be substituted for the SiS 961 chip from the SiS 645 family.
The memory controller
The heart of SiS 648ís North Bridge lies in its memory controller. Like previous SiS memory controllers, SiS 648 supports both synchronous and asynchronous bus speed operation. This means that the memory bus and system front-side bus can operate at the same speed or independent of each other. In particular, eight multiplier options are available for the memory bus, which can make things intimidating for the inexperienced computer user. With two system bus options to chose from (100MHz or 133MHz if you want to remain in spec) and four different memory types (DDR200, DDR266, DDR333, and DDR400) this adds for up to eight different combinations, ensuring support for every flavor of Pentium 4 system available.
The South Bridge
As we stated earlier, motherboard manufacturers have two South Bridgeís to choose from for SiS 648: SiS 963 or SiS 961. The SiS 961 chip is borrowed from the SiS 645/SiS 645DX chipsets, and as such will likely only be used on SiS 648 motherboards intended for the value market. When the SiS 648/SiS 961 combination is used, bandwidth between the North Bridge and South Bridge is 533MB/sec, the same figure available on SiS 645/SiS 645DX. If SiS 963 is implemented, bandwidth jumps to 1GB/sec between both chips. In order to support this, SiS had to add a few pins to SiS 963, so it isnít pin-compatible with the SiS 961 South Bridge.
In particular, the pathway between the North Bridge and South Bridge is 16-bits wide and operates at 533MHz when the SiS 963 chip is used. Like SiS 645, the link between both chips is bi-directional. This means that two independent pathways have been implemented. One connection can send data from the SiS 648 chip to SiS 963, while the second pathway can simultaneously send data to SiS 648 by way of the SiS 963 South Bridge. In comparison, both Intelís 845E and VIAís own P4X333 chipsets offer 266MB/sec between both chips (although VIAís recently announced P4X400 chipset offers 533MB/sec of bandwidth).
One new feature SiS 963 adds is support for the new USB 2.0 protocol. Offering up to 480MB/sec of bandwidth, USB 2.0 offers 40 times more performance than USB 1.1. Of course, USB 2.0 is backwards compatible with USB 1.1 devices; no new cables or connectors are necessary. Up to six USB devices are supported by the South Bridge.
The SiS 648 reference motherboard
The board layout of the SiS 648 reference motherboard is slightly different than the SiS 645DX board. Minute component changes were made, although at a quick glance some enthusiasts would hardly notice the difference.
Stability of the reference board was excellent. We didnít encounter a single lockup or crash in Windows XP during our testing while we were running the system within spec. When we attempted to run three DDR333 modules on the SiS 648 system some applications would occasionally crash, kicking us back to the Windows desktop but not locking up the system. The chipset doesnít officially support three DDR333 modules, so the fact that it would run many Windows applications with no problems was a pleasant surprise, but we wouldnít recommend it for consumers in mission-critical applications.
We mixed and matched many DDR266 and DDR333 modules from a wide variety of manufacturers and didnít encounter any problems with the SiS 648 reference board. Weíre still unsure how well DDR400 memory will ultimately run on the SiS 648 platform, as the only module we have was supplied by SiS for our testing.
Since we just discussed memory modules, weíll start there first. As we just stated, SiS supplied us with a DDR400 module manufactured by TwinMOS Technologies. TwinMOS is a relatively new memory manufacturer that is based in Taiwan and is primarily available in the Asian market. TwinMOS DDR400 modules are in full production now and should begin slowly trickling onto the market, although weíre unsure if that applies to those of us here in the US. Besides TwinMOS, KingMax, Mushkin, and Corsair Microsystems are also currently shipping DDR400 memory modules.
Intel Pentium 4 2.53GHz
ABIT TH7II-RAID (for 1066MHz RDRAM tests)
SiS 645DX reference motherboard
SiS 648 reference motherboard
256MB Corsair XMS DDR333 CAS2 SDRAM
256MB TwinMOS CAS2.5 DDR400 SDRAM
256MB PC800 RDRAM
NVIDIA GeForce4 Ti 4600 reference board
Driver version Detonator 28.32
30GB IBM Deskstar DTLA 307030 ATA/100 Hard Drive
AFREEY 12X DVD-ROM
Windows XP Professional
Desktop Resolution: 1024x768x32
3DMark 2001 Second Edition - 32-bit color, 32-bit textures
3DMark 2001 - DirectX 8
Despite giving up roughly a gigabyte of bandwidth to 1066MHz RDRAM, the DDR400-based SiS 648 testing system comes out on top in 3DMark 2001SE. The margin is ultra slim though, less than 1% at all resolutions. When equipped with DDR333 memory performance drops off three percentage points at 1024x768x32, but it still offers enough performance to outrun Intelís 850E chipset when paired with PC800 RDRAM.
3DMark 2001 - Car Chase
3DMark 2001 - Dragothic
3DMark 2001 - Lobby
3DMark 2001 - Nature
Serious Sam 2 - OpenGL
SiS 648 continues to outperform the 850E/PC1066-based Pentium 4 system when outfitted with DDR400 SDRAM with Serious Sam. At 800x600x32, we witnessed a 2% performance advantage for the SiS platform. As we saw in 3DMark 2001SE, even the DDR333 SiS systems are able to outperform the PC800 RDRAM 850E platform, although DDR333 only gives up 500MB/sec of bandwidth to RDRAM, and keep in mind DDRís lower latency.
Quake III - High Quality
In Quake 3 the final results remain the same, although the i850E Pentium 4 platform is able to gain slightly on SiS 648 with DDR400 memory. SiS 648 continues to offer about 1.5% more performance than its predecessor, SiS 645DX when the test conditions are the same, indicating that SiS has indeed implemented some improvements in SiS 648ís memory controller.
Jedi Knight II
The SiS 648 platform lands a clean sweep in all our gaming tests, coming out ahead again in Jedi Knight II.
SYSmark 2002 tests give the edge to SiS 648, although the margin overall is only one percentage point. The margins on all of these systems are incredibly slim, in SYSmark 2002ís Internet Content Creation test DDR400 only yields a one percent performance advantage over DDR333. Quite simply, if youíre going to be sticking to a lot of desktop applications, you might as well save a few bucks and stick with DDR333 memory for now.
Itís looking like SiS has another successful product on its hands with its SiS 648 chipset. Like all of SiSí previous Pentium 4 chipsets, performance is excellent, as is reliability. There really isnít much to say against the SiS 648 chipset. Sure the memory compatibility question with DDR400 is still up in the air (especially since one true standard doesnít exist), but this isnít a criticism that you can aim at SiS, memory manufacturers definitely share some of the blame. Now that the platform is out there the compatibility question should be answered pretty quickly. For its part SiS has been testing their SiS 648 chipset with a wide variety of memory modules.
In a similar sense, you could also criticize the lack of support for more than two DDR333 memory modules. But again, this isnít a limitation that is unique to SiS, Intelís own DDR chipset only supports two memory banks (although many motherboard manufacturers are shipping motherboards with three DIMMs) and end users have definitely had their fair share of problems with VIA-based DDR chipsets and multiple memory modules.
So what cons can we find that are unique to SiS and its SiS 648 chipset? As far as we can tell, the only criticism we have with the chipset is that it isnít available right now. Our tests indicate that SiS 648 isnít just an excellent performer; itís the fastest platform available for the Pentium 4 right now. While DDR400 memory modules donít provide quite as much bandwidth as 1066MHz RDRAM on paper, SiSí implementation with the SiS 648 chipset offers largely all of the bandwidth of RDRAM in our tests with SiSoft Sandra. When you combine this with the inexpensive price weíre expecting most SiS 648 motherboards to go for (right around the $100 price point), the choice becomes a no-brainer.
Now weíre just hoping that motherboard manufacturers wonít use the inexpensive price of the SiS 648 chipset as an excuse to position their SiS 648-based products solely in the value segment. Weíre hoping for fully loaded SiS 648 motherboards with six PCI slots, onboard IDE RAID, and plenty of overclocking options for the overclocking community. SiS has delivered a platform with cutting-edge performance at an incredibly low price point. Now itís up to motherboard manufacturers to fulfill their end of the equation and bring equally powerful products to market without breaking consumers wallets.
SiSí experience with the Pentium 4 platform and DDR memory really shows in the SiS 648 chipset. Even Intelís own DDR platforms are ages behind in features and performance. SiS deserves a lot of credit for bringing such an impressive product to market so quickly. Itís no small wonder why SiS has seen so much success over the course of the past 12 months.
SIDEBAR: Are you as impressed as we are with the SiS 648 chipset or do you plan on holding out for something more? Speak with others in the comments!
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