S3 Graphics' multi-GPU technology Multichrome explored

Multichrome is S3's answer to SLI and Crossfire. At best, it is comparable with Atis "software" Crossfire, because two Chrome S2x cards communicate exclusively via the PCI Express interface with each other; there are no bridges. Similar to the multi-GPU solutions of the two big ones (AMD, Nvidia), S3 is also using AFR (Alternate frame rendering) and the slower technology SFR (Split Frame Rendering) to balance the work. The GPUs alternately calculate different frames, and therefore achieve at least theoretically a performance doubling. We have to mention that Multichrome is also struggling with the now infamous "micro stuttering", but this issue, we will devote separately.


Testbed
We test in the following two Chrome S27 cards, each with 128 MiByte VRAM under Windows XP SP2. A Gigabyte DS3P-965P is the basis, which has a PCI-E x16 and a x4 slot. The latter has probably a slowdown effect on the communication between the two cards, which exclusively relies on the PCI-Express. We will do further tests on an X38 board, and in the case of gross deviations publish the results.

The handling of multichrome is simple enough: install cards, install drivers, activate multichrome within the driver panel - that's it. The latter is reliably and without rebooting, which is a very positive experience with SLI and Crossfire and their problems in mind.

With multichrome there is a simple exe-recognition. So many games are not recognized by the driver automatically and only use a single GPU. Here it helps to rename the execution file in 3DMark03.exe, 3DMark05.exe or Oblivion.exe, whereupon multichrome activated. This trick helped us with World of Warcraft, Crysis, Stalker and Flatout 2.

Performance and scaling
As the two big ones invest a lot of financial and programming power into SLI/Crossfire, you cannot expect too much from S3. Like SLI and Crossfire, multichrome shows a mixed picture. Depending on the application, a duo of two S27 cards scale up to 100, but often only 30 percent. And sometimes AFR / SFR even acts counterproductive - like in 3D Mark 06 (see benchmarks). The best "optimized" was apparently 3D Mark 03, because here two S27 are almost twice as fast as a single one.




This beautiful prelude is not followed by the gaming benchmarks. Fear gains an average of 38 percent by Multichrome, but the minimum Fps fall down reproducible. The Source Engine works out better: Half-Life 2 is about 30 percent faster in 1024x768 (with 5x/9x SSAA and 16:1 AF even 90 percent!) and Lost Coast as well as World of Warcraft gained by almost 50 percent.

Summary
If Crossfire and SLI are too immature for you, you should stay away from two Chrome cards. Most games need to be renamed and scale not too good. Moreover, the stuttering effect is always present.

If you still like to do something special, we recommend Ebay. S27 cards are no longer in retail, but the smaller Chrome S25 with insane 512 MiByte VRAM are to be but found at the online auction house. The difference to the tested S27s are primarily the reduced clock rates: 500/400 MHz instead of 700/660 MHz. At 30 euros x 2, you may enter the world of Multichrome.