Overclocking: Nvidia’s Success

Previous Nvidia chipsets for Intel processors didn’t boast any overclocking records. It was really hard to increase their FSB frequency above the nominal value and the system would lose stability very quickly. With the new Nvidia nForce 680i SLI chipset Nvidia claims they are offering great overclocking experience. The new SPP is claimed to be stable at the FSB speeds far beyond the nominal values and should also work fine with the CPUs supporting 333MHz nominal FSB frequency.

Of course, we couldn’t miss the opportunity to check out these brave claims, so we devoted a special section of our review to investigating the mainboard performance at higher processor bus speeds.

The BIOS Setup of the reference Nvidia nForce 680i SLI based mainboard offers pretty rich set of overclocking friendly adjustable parameters. In fact, this mainboard can be compared with the best overclocking friendly mainboards out there. Here is a list of parameters that you can play with in the BIOS Setup during overclocking:

• You can change the FSB frequency from 100 to 625MHz with 1MHz stepping;
• The PCI Express bus frequency can be adjusted independently for all busses;
• You can independently adjust the frequency of the HyperTransport bus connecting the SPP and MCP;
• The CPU voltage can be adjusted from the nominal value to 1.8V with 0.0125V stepping;
• The FSB Termination voltage can be adjusted from 1.2V to 1.5V with 0.1V increment;
• The DIMM voltage can be adjusted from 1.8 to 2.5V with 0.05V stepping;
• SPP voltage can be adjusted from 1.2V to 1.55V with 0.05V increment;
• The MCP voltage can be adjusted from 1.5V to 1.755V with 0.025V increment;
• The HyperTransport bus voltage can be adjusted from 1.2V to 1.55V with 0.05V increment.

At first glance this list is pretty extensive. These functions should be more than enough even for extreme CPU overclocking experiments.

By the way, among the options offered in the BIOS Setup there is a setting that allows disabling processor cores independently, which may also be helpful for setting overclocking records.

For our practical tests we assembled a system around the Nvidia nForce 680i SLI based reference mainboard and Intel Core 2 Duo E6300 CPU working at 1.86GHz nominal speed. The system was also equipped with 2GB of Corsair TWIN2X2048-8888C4DF (Dominator) memory. The CPU was cooled down with Zalman CNPS9500 LED cooler and the PowerColor X1900 XTX 512MB represented the graphics subsystem.

Our first task was to determine the maximum FSB frequency when the Nvidia nForce 680i SLI based platform would remain stable. In order to eliminate possible issues right from the start we clocked the memory synchronously with the FSB and the timings were set to 4-4-4-12-2T.

To our great satisfaction the reference mainboard easily surpassed 333MHz FSB, as well as 400MHz FSB. However, after that overclocking didn’t go any further, and the board wouldn’t boot at 450MHz FSB. We were pleased with the fact that the after freezing on the POST stage the mainboard would restart with “safe?parameters so that we could get into the BIOS Setup and adjust the settings. This extremely useful function functions saves you a lot of time during testing, because you don’t have to reach for Clear CMOS jumper.

As we continue our overclocking discussion, we would like to remind you that Core 2 Duo E6300 processor used to work stably at 500MHz FSB on the best overclocker’s mainboards for LGA775 form-factor based on Intel P965 Express chipset. Therefore, it is evident that something new has hindered further overclocking on our Nvidia nForce 680i SLI based mainboard. Unfortunately, we couldn’t figure out what the problem was in this case. We couldn’t get beyond that point even after raising the processor Vcore, chipset voltage and bus voltages. All we could do is find that maximum FSB speed when the mainboard could boot safely. As we have found out almost immediately, the system boots and works absolutely stable at 449MHz FSB frequency. However, if we added at least 1MHz in the BIOS Setup, the board couldn’t pass the POST stage.

I think that it could be the not completely finalized BIOS that is responsible for this situation, things could improve with the future BIOS versions.

However, as of today we have to admit that Nvidia nForce 680i SLI based mainboards are a less efficient for processor overclocking than the solutions on Intel 975X Express and Intel P965 Express.

The second thing we studied during our overclocking experiments was results of memory overclocking on Nvidia nForce 680i SLI based reference platform. We decided to perform this test because contemporary mainboards on Intel chipsets available in the today’s market demonstrate absolutely different results when the memory bus frequency is increased. In particular, Intel P965 Express based mainboards support much higher memory bus frequency than Intel 975X Express based ones, which we have already mentioned in our article called Choosing the Right Memory for Core 2 Duo Platform - Part 2: DDR2-1000, DDR2-1067 SDRAM.

Within this series of experiments we decided to overclock our Corsair TWIN2X2048-8888C4DF (Dominator) kit that could hit 1152GHz in ASUS P5B Deluxe mainboard with 4-4-4-12 timings and 2.4V voltage (see our article called DDR2 SDRAM to Hit 1.1GHz: Corsair Dominator vs. OCZ PC2-8800 Gold Edition).

We didn’t clock the memory bus on our Nvidia nForce 680i SLI based mainboard asynchronously. We tried to hit higher speeds by adjusting the dividers and FSB frequency.

During our test session we managed to make a few very interesting conclusions. Firstly, when the memory frequency exceeds 800MHz, 1T Command Rate causes system instability. In other words, if you raise the frequency, then you should raise the Command Rate setting, although in this case the system may lose about 2-3% of its performance.

The second conclusion also turned out not very optimistic. Our mainboard failed to let the memory work at the same frequency as on Intel P965 Express mainboard we used before. Nvidia nForce 680i SLI reference solution allowed the memory to work at 1098MHz maximum, no higher than that. Although the system would still start at even higher DDR2 SDRAM memory frequency, the system would still fail the stability tests.

As a result, we can only conclude that Nvidia nForce 680i SLI cannot yet compete with Intel P965 Express, especially its new C2 revision, in terms of overclocking potential. At the same time, I have to stress that Nvidia nForce 680i SLI has considerably improved its overclocking friendliness since the times of nForce 590 Intel Edition. Moreover, we still hope that future BIOS versions as well as the mainboards based on manufacturers?own design may be free from the problems we encountered today during our overclocking session.