Our CPU overclocking experiments were performed in the following test platforms:
- Mainboard: ASUS P5N-D, rev. 1.02G, BIOS 0502;
- Intel Core 2 Duo E8400 (3.0GHz, 333MHz FSB, 6MB, Wolfdale, rev. C0);
- Intel Core 2 Quad Q9300 (2.5GHz, 333MHz FSB, 6MB, Yorkfield, rev. M1);
- Memory: 2x1024MB Corsair Dominator TWIN2X2048-9136C5D;
- Graphics card: NVIDIA GeForce 8800 GTS 320MB;
- HDD: Seagate Barracuda 7200.10 (ST3320620AS) - 7200RPM, 16MB, SATA 320GB;
- CPU cooler: Zalman CNPS9700 LED;
- PSU: Antec NeoPower HE 550 (550W).
I have to say that we haven’t heard anything inspiring about Nvidia nForce 750i SLI based mainboards. They were claimed to have lower maximum stable FSB frequency than Intel based mainboards, to have performance hits and non-operational frequency intervals. At first we decided to find that maximum FSB frequency when the mainboard would remain stable. We lowered the processor clock frequency multiplier, set the memory into synchronous mode, increased the processor Vcore, Vchipset, Vmem and HyperTransport voltage. Just in case we lowered the HyperTransport bus frequency.
We failed to get the board to boot at 450MHz FSB. AT 425MHz FSB we loaded Windows, but the system hung right after the CPU-Z launch. And even at 400MHz FSB the mainboard didn’t seem to work confidently. However, everything changed once I started increasing the FSB frequency instead of reducing it. The board passed all Prime95 short-term tests at 425MHz and then at 450MHz and even 475MHz FSB. We had to increase NB voltage from 1.4V right to 1.6V only to ensure stability at 500MHz FSB. However, it turned out to be the maximum: the mainboard wouldn’t stay stable neither at 525MHz nor at 510MHz FSB.
Well, 500MHz FSB is not enough for overclocking the youngest CPUs with low clock frequency multipliers, so it is not the best result we could have achieved. However, we obtained it in very sparing conditions, when the CPU frequency didn’t exceed the nominal, since we lowered the clock frequency multiplier. So, will this mainboard be able to overclock a dual-core processor?
The results of our Intel Core 2 Duo E8400 overclocking experiments performed on different mainboards vary between 4.05GHz and 4.1GHz. In other words, for the nominal x9 frequency multiplier the FSB speed should be pushed to 450-455MHz. The system failed at 455MHz FSB: the mainboard started but didn’t boot Windows. However, at 450MHz FSB the system remained stable in Prime95 load test for some time.
Partially satisfied with this preliminary result I decided to continue next day. However, in the morning the mainboard refused to boot at all, although nothing has been changed since last night. I recalled that last night I managed to get to pretty high FSB frequencies by starting low. So, I lowered the FSB setting. The mainboard worked for some time, warmed up and started just fine at 450MHz. As for 455MHz, I still couldn’t get the board to work at this FSB frequency.
I can hardly imagine an overclocker who would be willing to “warm up” the mainboard at low FSB speed, like a car in winter, in order to later on enjoy the advantages of maximum overclocking. Looks like ASUS P5N-D cannot really boast much here.
I had to check out one more rumor about Nvidia nForce 750i SLI chipset claiming that somewhere between 450-480MHz FSB there is FSB Strap, i.e. the performance drops dramatically. We already know the parameter settings with which ASUS P5N-D mainboard is operational up to 500MHz FSB frequency. So, we used these settings, lowered the processor clock frequency multiplier, locked the memory timings. We tested the memory subsystem in Everest program starting with 400MHz FSB and moving up with 10MHz increments in order to detect at what frequency the performance will drop. Up to 440MHz performance grew gradually and at 450MHz… No, no drop, the mainboard just stopped working.
I would have also stopped working with an unstable board like that, but I had to check out its performance during quad-core processors overclocking. If it couldn’t overclock a dual-core CPU, then it should definitely fail the quad-core. So, the obtained results were not surprising at all. I used an Intel Core 2 Quad Q9300 that is capable of working at 475MHz FSB on good mainboards. My attempt to start the system with this processor failed at 440MHz FSB, as well as at 430MHz. I decided not to go any lower, because it didn’t really make any sense already.
I could probably get very frustrated with overclocking-unfriendly ASUS P4N-D mainboard. However, these mainboard tests performed a purely control function. A few days earlier I checked out MSI P7N SLI Platinum mainboard based on the same Nvidia nForce 750i SLI chipset. The results of our overclocking experiments were very disappointing: maximum stable FSB frequency for a dual-core processor was only 485MHz, and a quad-core CPU didn’t overclock at all. That is why I decided to check out ASUS P5N-D mainboard to see if it was MSI’s fault or Nvidia’s weak chipset. Looks like a lot of problems lie in the chipset. No wonder, since it is built on not very new Nvidia nForce 6 core logic.
However, in order to make any final conclusions I had to test a reference mainboard and luckily, I got this opportunity. I believe “FTW” in the name of EVGA nForce 750i SLI FTW mainboard stands for “Engineered For The Win”. Or maybe the slogan was offered for the abbreviation, it doesn’t really matter. What matters is the mainboard’s inability to overclock.
The board looks very attractive, but is hardly an overclocker product. ASUS mainboards have really smart BIOS. It doesn’t interfere during not very aggressive overclocking and then starts increasing the processor and chipset voltages little by little. The BIOS of EVGA nForce 750i SLI FTW mainboard is not that smart. It raises the voltage even during most insignificant overclocking disabling power-saving technologies in this case. It is even worse than by ASUS mainboards. Besides, with the Intel Core 2 Duo E8400 processor multiplier lowered to x6 the mainboard could only start and boot the OS at 425MHz FSB, not any higher. So, no wonder that ASUS an MSI preferred to develop their own mainboard design, although they still failed to cope with the tricky Nvidia nForce 750i SLI chipset.