Overclocking and Stability

Overclocking the 790i

We had moderate luck overclocking our 780i SLI board from ASUS. Using an Intel Core 2 Duo E8500, we hit a 1750 MHz front side bus. That was good enough to run all of our benchmarks stably, but the board wouldn’t go any further. We dropped the chip’s multiplier, tweaked voltages, and set slower memory bus speeds—all to no avail. For all of the Striker’s fancy features and extravagant copper, its engine was capped. Our only hope was that the 790i could push us a bit further.

And push it did. We started right where we left off with the 780i and saw success. From the initial 1750 MHz setting, we inched the bus past 1830 MHz with a 9x multiplier. At the end of the day, we were looking for a solid mix of clock speed, front side bus performance, and, at NVIDIA’s recommendation, synchronous operation with the memory bus. The magic combination was 1800. At the E8500’s full 9.5x multiplier, we were able to set a synchronous 1800 MHz front side bus, 1800 MHz memory bus, and still get reliable operation at 4.28 GHz.

Three PCI Express x16 slots, two PCI Express x1 slots, and a pair of standard PCI slots cover all of the bases

Dual Broadcom Gigabit PHY

The resulting combination delivered breathtaking performance. If there’s a reason to spend the extra money on a 790i and DDR3 memory, it’s what you can do beyond the platform’s stock speeds.

SLI and Stability

We recently switched our test systems over from a single graphics card to a dual-card configuration. That way, when we run higher-resolution benchmarks, we’re more likely to see the impact of the CPUs and platforms we’re testing, rather than a brick wall as those more intense settings peg our graphics cards.

With a single GeForce 8800 GT in the 790i board, everything ran as planned. However, when we’d install a pair of the cards and set them to run in SLI mode, it’d sometimes take three or four attempts to get each benchmark to finish. Each time, the error would read, “Display driver stopped responding and has recovered.”

There are new drivers available from NVIDIA, but keep in mind that those are for the company’s newest 9-series cards. Older 8-series boards are still using the 169.25 package from December of last year. Almost certainly, the stability issues we were seeing are caused by NVIDIA’s driver software, known to have made a painful transition over to Vista.

So much for the platform concept, where devices developed under the same roof run better together.

It’s also worth noting that the latest BIOS from NVIDIA features two obliquely documented settings: P1 and P2. Apparently, they both optimize certain timing settings in the 790i SPP. We found from OCZ, though, that enabling either setting will prevent stable operation at higher memory frequencies. They should thus be left at “Auto” rather than “Enabled.”