An update on AMD 790FX motherboards

We weren’t particularly impressed with AMD’s 790FX chipset when we took our first look at it last month. The Gigabyte GA-MA790FX-DQ6 motherboard we tested had numerous issues, including BIOS quirks and relatively high power consumption. The chipset itself appeared flawed, as well, exhibiting slow USB and PCI performance and compatibility problems between Windows Vista and Serial ATA drives running in AHCI mode.

To gather a broader impression of the 790FX, we’ve rounded up new motherboards based on the chipset from Asus and MSI to see how they compare with Gigabyte’s initial offering. We’ve also dug deeper into the SB600’s support for AHCI in Vista, discovering some troubling performance characteristics along the way. Keep reading for a quick look at the current 790FX motherboard landscape.

New boards from Asus and MSI
With a street price hovering around $265, Gigabyte’s GA-MA790FX-DQ6 comes in at the very high end of the 790FX motherboard spectrum. There, it’s joined by Asus’ M3A32-MVP Deluxe WiFi-AP Edition, which can be had for about $35 less. At the other end of the map we find MSI’s K9A2 Platinum selling for as little as $156—clearly the bargain of the three. Time constraints prevent us from giving these boards a full work-up. We’ve run them through our full chipset test suite, though, and have a complete set of results to report.

These boards are pretty much what you’d expect from their respective manufacturers. The Asus is packed to the gills with onboard peripherals, including an 802.11g Wi-Fi module. Asus manages to squeeze four PCIe x16 slots onto the board while ensuring that monster graphics cards won’t obscure access to onboard ports, as well.

Adding to the recent trend toward elaborate chipset coolers, Asus bundles a memory cooling module with the board that links memory modules to the chipset heatpipe network. This adjustable memory heatsink is designed to be used in lieu of traditional DIMM heat spreaders, but it only works with two modules at a time.

As one might expect, the MSI board is quite a bit more subdued, lacking Wi-Fi and fancy memory cooling. MSI still manages to squeeze in four PCIe x16 slots, though, and they’re spaced to allow for four double-wide graphics cards. However, longer double-wide cards installed in the second PCIe x16 slot will obscure acess to some, if not all, of the board’s SATA ports. Note that the K9A2 Platinum locates the north bridge chip slightly to the left of the CPU socket rather than directly below it.

Specifications compared
To allow for quick comparison, we’ve summarized the specifications of the M3A32-MVP Deluxe and K9A2 Platinum below.

Given the price difference between the boards, the MSI’s specs certainly look promising. About the only integrated peripheral it lacks is Wi-Fi, and it even manages one more expansion slot than the M3A32-MVP. The boards use different chips to provide auxiliary storage, Firewire, and Gigabit Ethernet, though. As you’ll see in a moment, there are clear differences in peripheral performance between them.

Neither the Asus nor the MSI board exhibited any BIOS irregularities during testing. The M3A32-MVP does provide a slightly more extensive array of overclocking options, though.

The Asus BIOS’s advantage comes in the voltage department, where it provides access to a much greater range of CPU overvolting options. It’s also possible to tweak a greater number of M3A32-MVP voltage variables. However, the K9A2 is better equipped for memory overclocking thanks to its higher memory voltage ceiling. MSI’s processor fan speed control is a little better than what you get with the Asus board, too, thanks to the ability to set a temperature target and fan speed percentage arbitrarily.

Benchmark results
We used an identical test configuration to that of our 790FX chipset review. The latest BIOS revisions were used for the Asus and MSI boards—revision 0603 and 1.1, respectively. As you’ll see, performance doesn’t vary much from board to board until you get into peripheral testing. We’ll save our commentary for the conclusions.

Memory performance

STARS Euler3d computational fluid dynamics

Worldbench

Gaming

Serial ATA performance

USB performance

Firewire performance

Ethernet performance

PCI Express performance

PCI performance

Power consumption

Overclocking

In testing, we were able to get the M3A32-MVP Deluxe stable with a 340MHz HT clock before the system refused to post.

The K9A2 Platinum fared nearly as well, sailing up to a 330MHz HT clock before flaking out. In both cases, the boards achieved their highest HT clocks with stock voltages. Additional juice didn’t help them scale any higher.

AHCI issues
A documented compatibility problem between Windows Vista and the 790FX chipset’s SB600 south bridge component currently complicates running drives in AHCI mode. As Microsoft notes:

When you try to install Windows Vista on a portable computer that uses an ATI SB600 Series chipset, each driver may take a long time to install. Therefore, the Windows Vista installation process may take several hours.

That’s if it works at all. One can install Vista by putting the SATA controller into IDE mode, but AHCI mode is necessary to take advantage of Native Command Queuing and SATA device hot-swapping, so it’s not a trivial capability to lose.

With a hotfix from Microsoft, we were able to get drives running in AHCI mode on both boards. However, doing so quickly all but requires an auxiliary storage controller. Vista must be installed with the south bridge running in IDE mode. You then have to move the hard drive to a secondary controller, switch the south bridge to AHCI mode, and apply the hotfix and necessary drivers before swapping the drive back. This problem should be resolved by Vista Service Pack 1, but without slipstreaming, that won’t necessarily make the installation process any easier.

The 790FX chipset’s AHCI problems don’t end with installation, though. There are also some performance oddities that we can illustrate nicely with IOMeter. In the results below, the 790FX is shown with the SB600 running in IDE mode, in AHCI mode with Windows Vista’s drivers, and in AHCI mode with 2.5.1540.47 drivers provided by AMD. Incidentally, those drivers come from Silicon Image, which is apparently responsible for the SB600’s Serial ATA controller.

With AMD’s official drivers, performance doesn’t scale at all as the load increases—even IDE mode offers higher transaction rates. Windows Vista’s native drivers seem to have it right; SB600 performance ramps more aggressively than even the nForce 590 SLI.

AMD’s official drivers also deliver much slower response times, suggesting that Vista’s native drivers may be the way to go.

Except for one little problem: CPU utilization. Vista’s native drivers may offer the AHCI performance we’re used to seeing, but they exact a huge CPU utilization penalty in the process. Silicon Image’s AMD’s drivers offer competitive CPU utilization, at least, but we’ve already seen that their performance is lacking.

At the moment, running the SB600 in AHCI mode requires choosing between poor performance or high CPU utilization. Neither is acceptable in our opinion, especially since competing chipsets seem to have no problems getting it right. Let’s hope AMD can address this issue with its upcoming SB700 south bridge.