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S3's MultiChrome dual-GPU technology
"MultiChrome is still more hassle-free and stable than either SLI or CrossFire were upon their initial public releases." "The MultiChrome rig draws only slightly more power than our test system with a single GeForce 6600 GT installed."
The Tech Report, 03 May 2006
S3 GRAPHICS HAS BEEN
making a slow, sustained push for respectability since the arrival of its first Chrome-series graphics processors in 2003. That push continued with the introduction of the updated Chrome S27 GPU last fall, and at that time, S3 hinted at a new wrinkle in its plans. Like ATI and NVIDIA, S3 would be introducing a multi-card graphics capability, dubbed MultiChrome. We got a brief preview
of MultiChrome in action back in November, but S3 has been quietly preparing the tech for prime time since then.
The time has come for MultiChrome to make its formal debut, and we've spent a few days playing with it in Damage Labs. Has S3 succeeded in doubling up on Chrome S27 GPUs for nearly twice the performance? Let's find out.
The Chrome S27 GPU
Before we get to talking about two of 'em, we should probably talk briefly in the singular about the Chrome S27 graphics chip. The S27 is a DirectX 9-class GPU ultimately derived from S3's original DeltaChrome design but enhanced in important ways over the years. S3's latest Chrome silicon includes a native PCI Express interface, 24 bits of precision per color channel throughout the graphics pipeline, and additional registers to speed execution of shader programs. S3 has a lower end version of this GPU called the Chrome S25, but only the S27 has S3's blessing for use in a MultiChrome config.
The basic graphics architecture of the Chrome S27 is fairly conventional. The GPU has four vertex shader units and eight pixel shader processors, but only four texturing units and four render back ends capable of turning a fragment into a pixel. Like most low-end GPUs, the S27 does have its compromises. Among them is a relatively simple memory controller with no crossbar design, and antialiasing capabilities that are limited to 2X or 4X ordered-grid supersampling. These limitations might be problematic in a more expensive product, but they're not show-stoppers here.
Like earlier iterations of the Chrome series, the S27 supports DirectX 9's Shader Model 2.0 programming model. That puts it slightly behind the curve compared to the latest GPUs from ATI and NVIDIA; those support Shader Model 3.0. The difference between the two programming models is complicated, but it essentially boils down to a few key things. SM3.0 allows for dynamic flow control in pixel shader programs, so that longer programs can fork and potentially take different paths depending on conditional results. Shader Model 3.0 also has a higher threshold for numeric precision, requiring datatypes as precise as 32 bits of floating-point data per color component in a pixel. Those are probably the two most important innovations in Shader Model 3.0, and they are simply not likely to mean much to a low-end graphics card at present. These cards simply aren't fast enough to use long, branchy shader programs to render effects complex enough to push the boundaries of SM2.0's required 24 bits of precision per color channel. For most intents and purposes, the Chrome S27 ought to be able to crank out visuals equivalent to those produced by its SM3.0-ready competitors—just as the Radeon X800 was able to keep pace with the GeForce 6800 when ATI and NVIDIA split on this issue.
Interestingly, S3 has chosen to have its Chrome S20-class GPUs manufactured by Fujitsu on a 90nm process. Thanks to this relatively advanced manufacturing technique, the Chrome S27 can run at a clock speed of 700MHz while keeping power consumption low. S27 cards ship with either 128MB or 256MB of GDDR3 memory, also clocked at 700MHz.
Those specs should do nice things for the S27, competitively speaking. The 256MB version of the S27 lives in the price neighborhood of the Radeon X1300 Pro and GeForce 7300 GS. At 700MHz, the Chrome S27 can pump out a peak of 2.8 billion pixels per second, each of them with a texture applied. The 700MHz memory clock gives the S27 a peak of 22.4 GB/s of bandwidth on its memory interface. By comparison, the Radeon X1300 Pro tops out at 2.4 billion textured pixels per second and only 11.2 GB/s of memory bandwidth. Any qualms about S3's less sophisticated memory controller should be erased by S3's use of much faster memory. The only real wild card here is pixel shader power. The S27 has eight of S3's shader processors running at 700MHz, while the X1300 Pro has four of ATI's more capable pixel shader units running at 600MHz. Pixel shader performance resists boiling down to basic math more than most things in graphics, because different architectures can have markedly variant delivered performance per clock.
That's a basic summary of the S27's place in the universe. We have a review of this GPU in the works, in direct comparison to the competition from ATI and NVIDIA, but in a quirk of scheduling, this brief look at MultiChrome is ready before that review. Stay tuned for a fuller look at the S27 in single-card form.
When they say Chrome, they mean it
Chrome goes Multi
S3 has wisely decided not to try and limit its multi-GPU solution to certain chipsets, despite the fact that S3 is owned by VIA. MultiChrome should therefore work on any motherboard with two PCI Express x16 slots, regardless of the core logic chipset onboard. Also, because it involves only low-end graphics cards, all MultiChrome configurations are "connectorless"—they don't require the use of an external dongle or bridge connection of any kind. Data are passed between the cards solely by means of a PCI Express connection, as has been the arrangement on some low-end multi-GPU configs from ATI and NVIDIA.
MultiChrome is right at home on the Asus A8R32-MVP Deluxe mobo
Like those other multi-graphics solutions, MultiChrome relies on a database of game profiles in order to determine when to do its thing and which load-balancing method to employ. S3 currently has profiles for about 50 games, including many of the more popular titles of the past few years. S3's drivers don't expose any back-door means for users to tweak or create game profiles themselves, so the existence of a profile will be crucial to MultiChrome's effectiveness. If the game doesn't have a profile, it will simply run on one card, without the performance benefits of dual GPUs.
Right now, S3 has only implemented one of the two most common load-balancing techniques used in dual-graphics solutions: alternate frame rendering (AFR). AFR is used widely because it offers the best performance scaling by boosting both vertex and pixel throughput. S3 says the other technique, split-frame rendering (SFR), is coming soon but isn't yet enabled in its current drivers. Without SFR, MultiChrome won't work with certain games whose rendering engines don't play well with AFR. I suspect that's why MultiChrome showed no performance benefit for us in Half Life 2.
We were also foiled in our attempts to test MultiChrome performance in Elder Scrolls IV: Oblivion by the lack of a profile for the game. In fact, we found that the game would crash from the graphics options menu with even a single Chrome S27 card. So long as I didn't change any graphics options, the game ran fine, but the crash was a disappointment. Oblivion itself isn't exactly known for being a rock of stability, so I hestiate to lay all blame at the feet of S3. Still, without a means of tweaking profiles, owners of MultiChrome rigs will be forced to rely on the volume and frequency of S3's profile updates in order to take advantage of that second card.
MultiChrome in action
MultiChrome itself is very simple to use. Simply check a box in the appropriate tab in S3's control panel, and it's working. It takes a second or two to initialize, but no reboot is required.
Yep. Do 'er. Thanks.
Once MultiChrome is enabled, you'll see a balloon help message each time the computer boots, indicating its status. This is more than vaguely reminiscent of how NVIDIA has chosen to notify the user about the presence of SLI, but that doesn't make it a bad thing. Users may turn off this indicator via the control panel if they wish.
Also much like SLI, MultiChrome can overlay a load balancing indicator on the screen in any 3D application. The indiciator is more intuitive and easier to read than NVIDIA's, but it doesn't offer any information about which load-balancing method is in use—not that it matters just yet.
That's the load indicator in the top-right corner
I may someday be cosmically punished for saying this, but MultiChrome has, well, polish. S3 is quite evidently aware of its underdog status in the graphics market, and the company has obviously taken care to refine its drivers before allowing early adopters and us press types to get our hands on them. The lack of support for split-frame rendering is not a trivial omission, but MultiChrome is still more hassle-free and stable than either SLI or CrossFire were upon their initial public releases.
About that third eye in the middle of your forehead..
Now that I've said something nice, I'll also point out something less pleasant. The true gamer who buys and owns an S3 Chrome S27 card will probably face notices like the following quite regularly, which we encountered during just a few days on hands-on testing with the cards.
To S3's credit, both of these games loaded up and ran just fine on the Chrome S27, with excellent image quality and smooth frame rates. Still, if it wants to appeal to gamers, S3 needs to hire a guy (or a few guys) to help make these kinds of notices go away. I was also disappointed to see that the high dynamic range lighting in Half-Life 2: Lost Coast wasn't functional on the S3 card. I understand Valve uses an integer texture format for its HDR algorithm that would probably work on the Chrome S27, if S3 worked with Valve to make it happen.
Why our tests are totally inappropriate—a little
Because we're working on a full review of the latest low-end graphics cards, including the Chrome S27, I shipped off all of my low-end cards to my esteemed colleague, Mr. Gasior, for testing. As a result, I was kind of at a loss to choose an appropriate pair of cards for comparing to the MultiChrome setup. The GeForce 7300 GS doesn't even support SLI, so that was out, and our only Radeon X1300 Pro had headed north via FedEx. My solution was to use a pair of slightly older cards based on NVIDIA's GeForce 6600 GT. The GeForce 6600 GT supports SLI and is still selling. When I was making the decision about what to test, the 128MB version of the 6600 GT was going for about $120, right where the Chrome S27 was priced.
But then S3 and Newegg dropped the Chrome S27 256MB's price to $99, sinking my like-priced comparison with a killer value torpedo. S3 is very careful about product positioning and would no doubt point out that the Chrome S27 competes more directly with the GeForce 7300 and the Radeon X1300, though the 6600 GT is as low as $115 at Newegg. Feel free to take the price gap into consideration when digesting the performance results.
Then there's the matter of moving data between the two cards. The 6600 GT uses an SLI connector, whereas MultiChrome relies on PCI Express. Honestly, I don't expect PCI-E bandwidth to be a serious hindrance to MultiChrome performance, but just to make it fair, we've tried a couple of different motherboards. Our primary test system uses an Asus A8N-SLI motherboard with eight PCI-E lanes going to each of its two graphics slots. We used this board in our main configuration because low-end cards like the Chrome S27 aren't likely to find their way into more expensive motherboards with 32 PCI Express lanes. However, we also ran some tests with the Asus A8R32-MVP Deluxe motherboard, based on ATI's CrossFire Express 3200 chipset, in order to see how the presence of a full 32 lanes of connectivity might impact MultiChrome performance.
Our testing methods
As ever, we did our best to deliver clean benchmark numbers. Tests were run at least three times, and the results were averaged.
Our test systems were configured like so:
Thanks to Crucial for providing us with memory for our testing. 2GB of RAM seems to be the new standard for most folks, and Crucial hooked us up with some of its 1GB DIMMs for testing. Although these particular modules are rated for CAS 3 at 400MHz, they ran perfectly for us with 2.5-3-3-8 timings at 2.85V.
All of our test systems were powered by OCZ PowerStream 520W power supply units. The PowerStream was one of our Editor's Choice winners in our last PSU round-up.
Unless otherwise specified, image quality settings for the graphics cards were left at the control panel defaults.
The test systems' Windows desktops were set at 1280x1024 in 32-bit color at an 85Hz screen refresh rate. Vertical refresh sync (vsync) was disabled for all tests.
We used the following versions of our test applications:
The tests and methods we employ are generally publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.
Before we get into the games, we'll start off with a couple of generations of 3DMark to establish some sense of how the Chrome S27 and the 6600 GT stack up. Please note that in the tests below, the MultiChrome config labeled "dual x16" is the one running on the Asus A8R32-MVP Deluxe mobo.
Our first indications are that MultiChrome scales well, not quite doubling the performance of a single card, but nearly doing so. Dual Chrome S27s also, impressively, prove faster than two GeForce 6600 GTs in 3DMark05. Surprisingly, going to a dual 16-lane PCI Express motherboard provides no real performance benefit for MultiChrome.
The Chrome S27 is handicapped in 3DMark06 by its lack of support for Shader Model 3.0. That hurts its overall score. However, in the SM2.0 index, the S3 does well, beating out the 6600 GT. Again, performance scales quite nicely in MultiChrome mode, and the A8R32-MVP's additional PCI-E lanes are apparently unneeded.
3DMark's synthetic tests give us a more granular look at how these solutions compare. Across the board, scaling from one card to two is excellent for both, and there's no performance gain for S3 in going with the CrossFire Xpress 3200 motherboard, even in the synthetic fill rate tests. The Chrome S27 looks very strong in the vertex shader tests, but not so strong in other areas. The 6600 GT has eight texture address units because its pixel shader ALUs handle that task, while the S3 has only four. The Chrome S27's higher clock speeds can't entirely make up the difference. Also, the NVIDIA card's eight pixel shader processors appear to achieve about twice the throughput of the Chrome S27's eight pixel shaders.
The Chrome S27 can't keep up with the 6600 GT here, but MultiChrome does achieve a decent performance boost. Image quality in Quake 4 on the MultiChrome config is impeccable.
We tested the next few games using FRAPS and playing through a portion of the game manually. For these games, we played through five 60-second gaming sessions per config and captured average and low frame rates for each. The average frames per second number is the mean of the average frame rates from all five sessions. We also chose to report the median of the low frame rates from all five sessions, in order to rule out outliers. We found that these methods gave us reasonably consistent results.
MultiChrome again scales well in F.E.A.R, boosting both average and median low frame rates.
The S3 card simply struggles in Battlefield 2. Adding a second card helps, but not enough to allow MultiChrome to equal the performance of a single GeForce 6600 GT.
Like the two above, we played this game manually and recorded frame rates with FRAPS. In this case, we're playing an online game, so frame rates were subject to some influence from an uncontrollable outside factor.
A single Chrome S27 achieves very acceptable frame rates in Guild Wars with the resolution and quality cranked up, but a second card does show some gains. Still, one GeForce 6600 GT is nearly as fast as two Chrome S27s.
We measured total system power consumption at the wall socket using a watt meter. The monitor was plugged into a separate outlet, so its power draw was not part of our measurement. The idle measurements were taken at the Windows desktop with AMD's Cool'n'Quiet CPU clock throttling function enabled. The cards were tested under load running our Quake 4 timedemo using the game's High Quality setting at 1600x1200 resolution. We turned off Cool'n'Quiet for testing under load.
At idle, the power consumption of the GeForce and Chrome cards is comparable. Once we fire up a game, though, the Chrome S27's lower peak power use becomes evident. The MultiChrome rig draws only slightly more power than our test system with a single GeForce 6600 GT installed.
MultiChrome leaves me feeling rather ambivalent. On the one hand, there are some clear positives. S3 has successfully cloned the functionality that NVIDIA and ATI have incorporated into their graphics portfolios over the past couple of years, and they've done so while apparently skipping the nasty teething stages that SLI and CrossFire had to endure while in public hands. I'm absolutely pleased with S3's decision not to lock down its multi-GPU tech to a chosen set of chipsets for business reasons, and I'm more or less convinced the choice to go "connectorless" and pass all data via PCI Express was the right one. MultiChrome scales well in the games it supports. Having played a handful of games on the Chrome S27 and MultiChrome over the past few days, I'm also gratified to see that S3 has avoided severely compromising image quality in order to boost frame rates. S3's graphics solutions are not in a class with those from ATI or NVIDIA, but they do appear to stand alone in third place, well ahead of the also-rans (including, notably, Intel's integrated chipset graphics.)
But I'm somewhat disappointed that the total peak performance S3 can offer when it combines two of its best GPUs isn't terribly compelling. I had really hoped going to dual GPUs would allow S3 to offer some form of solution that might appeal to PC gamers and enthusiasts. Too much has happened since MultiChrome was first announced, and that's simply not the case. There's just no way this is a $200 graphics solution on the order of the GeForce 7600 GT. Buy one of those cards and you'll be far ahead of what a pair of Chrome S27 cards can offer. Even the Chrome S27's seriously low power consumption is sullied by the fact of its performance—really, performance per watt isn't much better than that of the GeForce 6600 GT, an older 110nm GPU. And given that major game titles like Guild Wars and Half-Life 2 were throwing up warning messages about undetected hardware, I am wobbly on the prospects for S3 sustaining the kind of developer relations and game profiling efforts necessary to make MultiChrome a success over the long term. I hope they do it, and they deserve credit for getting as far as they have, but buying a MultiChrome rig for gaming is a big risk.
None of this is to say that MultiChrome might not have its place. As an upgrade from a single Chrome S27, MultiChrome is a solid option, so long as you're playing supported games. Also, if S3 maintains its support of this feature over the long term and further develops it, this technology could become a valuable tool when a newer, faster S3 GPU debuts in the future. Doubling up on a new product with a higher innate performance and a more competitive feature set could prove fairly potent—perhaps especially if they can squeeze two on to a single card. But for now, MultiChrome's virtues aren't sufficient to win an outright recommendation; you're better off looking to ATI or NVIDIA for a gaming graphics solution.