iXBT Labs - Computer Hardware in Detail






Single-channel chipsets for Pentium 4: SiS648FX and VIA PT800

The release of the single-channel i848P chipset with its unexpectedly outstanding characteristics, which had put Intel's Spring chipsets into an awkward position (they had two channels!) was a real success. In contrast to the past-oriented i865P with vague prospects, this chipset uses all features of Intel's modern south bridges and has no crippled north bridge components. One memory channel is locked but if 2GB RAM is enough for you, the only i848P disadvantage will be its speed.

What about the competitors? They have no dual-channel solutions for new processors (with 800MHz bus) to offer (the SiS655FX/TX and VIA PT880 chipsets are ready, but we still haven't seen any boards on them). At the same time, cheaper single-channel chipsets (the price was always an advantage of VIA and SiS) have been announced quite a long time ago, and today we are going to test the first SiS648FX and VIA PT800 solutions. But first, there's information on chipsets architectures. 


Its predecessor got some very high score in its time: at that moment it was the strongest competitor for i850E+RDRAM(PC1066) tandem, and SiS648-based boards with DDR400 support were cheaper than the top Intel+Rambus combination. Unfortunately, it had no Hyper-Threading support: the release of revision B had been postponed, and without such support the chipset wasn't of much interest among top solutions. Then the company released the dual-channel SiS655 (putting aside the SiS R658), which however hadn't set any new records. And after the announcement of Intel's new Pentium 4 line with 800 MHz FSB alongside a dual-channel chipset series, SiS had been keeping silence.

Today we're going to test the first serial mainboard on SiS648FX we got. The product hasn't obtained any considerable new features, so the company just added "FX" to the name. What's changed in SiS648FX comparing to SiS648? Have a look at its block diagram.

The picture from the SiS website is out of synch with reality :). First of all, SiS648FX officially supports DDR400 (in contrast to its predecessor). Second, 800MHz FSB support is not shown in the diagram at all. There are no more differences between the chipsets. The chipset is officially coupled with SiS963L south bridge, while SiS648 is coupled with its complete version - SiS963 (that is more expensive due to integrated FireWire). This situation perfectly illustrates the changes: while SiS648 has been developed to be a performance and functionality leader, SiS648FX is aimed at the low-end sector. Remember that all the latest south bridges from SiS are pin-compatible and have the same interface to north bridge, so mainboard manufacturers can easily replace them (if they want).

Here are chipset brief specs (the south bridge features are given for the recommended SiS963L):

  • Supports Pentium 4/Celeron with 400/533/800 MHz FSB
  • Up to 3GB of unbuffered DDR266/333 memory (3 modules), up to 2 GB of DDR400 (2 modules)
  • AGP 4x/8x
  • MuTIOL 1G (~1 GB/s) interface to the south bridge
  • 2 x Parallel ATA (ATA133) channels for up to 4 devices (SiS also offers an external SATA/PATA PCI controller chip - SiS180)
  • 6 x USB 2.0 devices
  • 6 x PCI Bus Master devices
  • Fast Ethernet MAC controller
  • Supports AC-Link and LPC link (that is common for all chipsets)

There's neither Serial ATA, nor FireWire. However, there's one more interesting feature we'd like to attract your attention to - HyperStreaming. This is SiS' proprietary technology integrated in all its latest chipsets. It's obvious that SiS began promoting its products using beautiful logos and esoteric terms. The matter is that all components of the HyperStreaming technology have been supported in SIS chipsets for over two years already and only now they are united under a single name.

The idea of this technology is that the north bridge memory controller can operate in several modes.

  1. One stream - minimal latencies. The results provided by SiS are obtained under the specific RTOS (Real-Time OS) and are as useful for ordinary users as Pentium 4 scores in Digger. In our tests we will compare SiS648FX with its competitors under Windows.
  2. Several streams - pipelined and concurrent execution, which accelerates total processing (in particular, it optimizes the number of virtual read/write channels). The company shows the advantage over the rival solution in the IOMeter test at operation with one or several hard drives. We won't use this test, but there will be several streams anyway (in games, for example).
  3. Priority stream - guaranteed bandwidth for streams that need isochronous data transfer (for example, networking or audio). Such functionality is also provided by other companies (in particular, by NVIDIA). It's rather difficult to test this feature.
  4. Always - intellectual transaction dispatcher (including f.i. out-of-order memory requests execution to access opened memory pages first). It should be effective for all tests sensitive to the memory performance, which are quite a number in our suite.

Well, there's nothing revolutionary actually, let's see what the real scores will be.


This chipset is the standard extension of VIA's Pentium 4 line. The line was renamed from P4X to PT for unification purposes (with KT series for Athlon XP) and got the "800" postfix (though it's meaning is not clear). Its P4X400 predecessor is reviewed here (note that boards on the new stepping of the chipset do support DDR400 memory, though it doesn't accelerate them in any way).

Here are chipset brief specs (VT8237 south bridge):

  • Supports Pentium 4/Celeron CPU with 400/533/800 MHz FSB
  • Up to 8 GB (4 modules) of DDR266/333/400 memory with/without ECC (ECC support is a pleasant surprise for VIA's chipset!)
  • AGP 4x/8x
  • 8x V-Link bus (533 MB/s) to the south bridge
  • 2 x Parallel ATA channels (ATA133) for up to 4 devices
  • 2 x Serial ATA channels (SATA150) for up to 2 devices
  • SATAlite interface for 2 more SATA devices (external PHY controller required)
  • VIA V-RAID for SATA RAID (0, 1, 0+1, JBOD)
  • 8 x USB 2.0 devices
  • 6 x PCI Bus Master devices
  • Fast Ethernet MAC controller
  • Support for AC-Link and LPC link is common for all chipsets

Compared to P4X400, it supports Intel's new processors, has better memory features (max. capacity, ECC support), uses a new south bridge with more USB2.0 ports and supports Serial ATA. If we compare VIA PT800 to its direct competitors (single-channel Pentium 4 chipsets), this will be the most functionally advanced chipset. So what about the performance?



  • Intel Pentium 4 3.2 GHz processor (16x200 MHz), Socket 478
  • Mainboards:
  • Memory: 2x256 MB PC4000(DDR500) DDR SDRAM DIMM OCZ, CL 2 in DDR400 mode
  • Video card: Manli ATI Radeon 9800 Pro 256 MB
  • Hard drive: Western Digital WD360 (SATA), 10,000 rpm (IDE-SATA SABR200HV adapter)


OS and drivers:

  • Windows XP Professional SP1
  • DirectX 9.0b
  • Intel Chipset Software Installation Utility
  • SiS AGP Driver 1.17
  • SiS IDE Driver 2.03
  • VIA Hyperion 4.49
  • VIA SATA Driver 2.10a
  • ATI Catalyst 3.7

Test applications:

  • CacheBurst32
  • 7-Zip 2.30b11
  • VirtualDub 1.5.4 + DivX codec 5.1 Pro
  • RazorLame + Lame codec 3.93.1
  • discreet 3ds max 5.1 + Splutterfish Brazil Rendering System 1.0
  • Adobe Photoshop 7.0
  • Gray Matter Studios & Nerve Software Return To Castle Wolfenstein v1.1
  • Croteam/GodGames Serious Sam: The Second Encounter v1.07
  • Digital Extremes/Epic Games/Atari Unreal Tournament 2003 v2225

Board ASUS P4P800S-E Deluxe DFI 648FX-ALE ABIT VI7
Links ASUS P4P800S-E Deluxe DFI 648FX-ALE ABIT VI7
Chipset Intel 848P (RG82848P + FW82801ER) SiS648FX (SiS648FX + SiS963L) VIA PT800 (PT800 + VT8237)
CPU supported Socket 478, Intel Pentium 4, Intel Celeron
Memory sockets 3 DDR 3 DDR 2 DDR
Expansion slots AGP/ 5 PCI/ ASUS Wi-Fi AGP/ 5 PCI AGP/ 5 PCI
I/O ports 1 FDD, 2 COM, 1 LPT, 2 PS/2 1 FDD, 2 COM, 1 LPT, 2 PS/2 1 FDD, 1 COM, 1 LPT, 2 PS/2
USB 4 USB 2.0 + 2 headers for 2 USB 2.0 2 USB 2.0 + 2 headers for 2 USB 2.0 4 USB 2.0 + 2 headers for 2 USB 2.0
FireWire 1 port + 1 header for 1 port (VIA VT6307) - -
Int. ATA controller ATA100 + SATA RAID ATA133 ATA133 + SATA RAID
Ext. ATA controller - - -
Sound Analog Devices AD1985 AC'97 codec C-Media CMI9739A AC'97 codec VIA VT1616 AC'97 codec
LAN controller Intel 82547EI (CSA Gigabit Ethernet) integrated Fast Ethernet integrated Fast Ethernet
I/O controller Winbond W83627THF-A Winbond W83697HF Winbond W83697HF
BIOS 4 Mbit AMI BIOS v2.51 2 Mbit Phoenix AwardBIOS v6.00PG 4 Mbit Phoenix AwardBIOS v6.00PG
Form-factor, dimensions ATX, 30.5x24.5 cm ATX, 30.5x20.5 cm ATX, 30.5x19.5 cm

Test results

First come the low-level memory controller tests, especially interesting due to Hyper-Threadi... oh sorry, HyperStreaming in the SiS chipset.

The latency is not low at all in the SiS648FX (well, SiS doesn't really compare 648FX with i848P and PT800 in its documentation). Judging by the data obtained, Intel's chipset might take the lead (with traditionally high write speed) and VIA's new solution might take the middle position. Now let's run our favorite benchmarks to reveal the real difference in the way memory controllers work.

The best benchmark is the one that compresses a large data volume with some archiver utilizing a complicated algorithm and a large dictionary that uses tens and even hundreds of memory megabytes. SiS falls behind by 16%, while PT800 yields less than 3% to the leader.

In case of MPEG4 encoding we don't have such difference: SiS648FX has caught up with VIA and even outscored it (i848P beats both by 3%).

Remember that not all applications depend on memory speed. For example, MP3 encoding depends exclusively on CPU clock.

One of the best external rendering modules for 3ds max (Brazil Rendering System) slows down SiS648FX a little (about 3%) comparing to its competitors.

The Photoshop scores look curious: VIA outscores SiS by 3%, but Intel 848P unexpectedly falls into the last place losing 1.5% to SiS648FX. We don't see any reasons for that. However, that was the only artifact during the tests.

You can see that all the game scores look identical. SiS remains an outsider, VIA PT800 outdoes it by 5-7%, and i848P by 6-10%.


All three single-channel chipsets for modern Pentium 4 processors (we don't consider ALi products) have very close north bridge characteristics. There's nothing to improve until they move to PCI Express, and the only difference is memory type and maximum capacity supported (but not the clock speed). VIA PT800 looks the best with its ECC support, which is a rare thing for budget chipsets (on the other hand, i848P has the CSA bus). South bridges might differ on different mainboards, but we'd like to distinguish VIA VT8237: ICH5 doesn't support Serial ATA RAID (though there's also ICH5R version), and SiS963L doesn't support Serial ATA at all (plus the FireWire lack).

The i848P is the fastest runner in this pack, though VIA PT800 yields only 3%. But remember that Intel's chipset was represented by the fastest board we tested, while for VIA chipset we only touched one model so far. SiS648FX loses 3 to 10 % (sometimes even more). Again, there's only one board based on this chipset in our testlab, but the gap is too great to be ignored. Taking into account the scarce functionality and low performance of SiS648FX among all three chipsets, its price is the most powerful feature. However, SiS has the newer dual-channel SiS655FX (which adds the 800 MHz FSB to a quite good SiS655) and its successor SiS655TX (which supports Advanced HyperStreaming). Well, the company does have dual-channel solutions to offer, and you might remember that Intel's dual-channel chipsets without PAT are quite close to i848P by performance, so don't take all that marketing rubbish about number of memory channels to your heart.

Serguei Pikalov (peek@ixbt.com)
Dmitry Mayorov (destrax@ixbt.com)

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