The HydraLogix chip aboard the Crosshair IV is an LT24102-A1 processor, as shown below. This chip is substantially more powerful than first-generation Hydra 100 processors. Compared to its predecessor, the LT24102 offers twice the bandwidth and can serve up to four x8 PCIe slots compared to just two x16 slots for the 100 series.
The Lucid processor incorporates a 32-bit RISC 'Diamond' processor built by Tensilica and clocked at 300MHz with a 64K L1 instruction cache and a 32K data cache. The diagram below shows how Asus has incorporated the LT24102 into the CrossHair IV Extreme.
Those would be GPU slots #2, #4, and #5
The Crosshair IV effectively contains two separate PCI-Express implementations. Users wanting to build a standard AMD CrossFire system are advised to use slots 1 and 3, both of which tie into AMD's 890FX controller. Enthusiasts who want to use more than three ATI GPUs (A-Mode), a mixed ATI/NV solution (X-Mode) or multiple Nvidia GPUs (N-Mode) should avoid slot three altogether. On paper, Hydra should be a drop-in replacement for Nvidia's SLI, but our performance tests were decidedly erratic.
Probing the Problem:
The major, full-stop problem with the Hydra engine is that it's currently impossible for us to predict either the degree of scaling Hydra will offer in a particular title or whether that title will be supported at all. When the Hydra Control Panel is first installed, it displays a list of more than one hundred ostensibly-supported titles. We can't comment on the accuracy of this list when using GT200, G92, or G80-based GeForce cards, but current support for Fermi-based products is limited.
After a great deal of benchmarking and repeated conversations with Asus and LucidLogix, we've compiled a list of supported (and unsupported) games and benchmarks using the 1.7.104a 64-bit Hydra drivers released on January 17, 2011. (We also tested the 1.7.103 drivers released in December and multiple WHQL driver releases from Nvidia).
||Unsupported Games (Using 1/17 Drivers):
* - Current support for 3DMark 11 is limited. All four GPU tests scale in Performance mode, but only one test scales across both GPUs in 'Extreme' mode.
** - Lost Planet 2 refused to run in DX11 at all, period. The game scaled in DX9.
*** - World of Warcraft refused to run in DX11 mode. It ran in DX9 mode but did not scale.
There's no common factor that separates the games that do work and those that should but don't. We discussed this at length with LucidLogix's Offir Remez, who pointed out that Lucid has been shipping hardware for barely a year, only recently added support for Fermi-based GPUs, and tests an enormous number of GPU configurations. He told us that Lucid is aware of the issues above, and he promised we'd have seen far more compatible games if we'd been testing with older GT200-based NV cards.
The Bottom Line:
We appreciate Lucid's willingness to openly discuss these support issues and agree that it takes time to ramp any multi-GPU solution; both SLI and Crossfire suffered significant growing pains in their early years. Understandable difficulties, however, don't change the fact that as of this writing, HydraLogix technology is not an effective SLI replacement.
We expect the number of Fermi-supported titles to improve as further drivers are released and believe that LucidLogix is committed to consistent driver improvement. Given sufficient time to bake, HydraLogix could one day provide a level of support substantially equivalent to SLI. For now, buyers looking for an SLI equivalent when using Fermi-class products should look elsewhere.