BIOS
Just as the 650i is a cut-down version of the 680i, so too are the BIOS options. Gone are the SLI Memory support and overclocking profiles. Most of the important options do remain, although a couple of the more advanced options controlling the northbridge and southbridge voltages as seen in the 680i motherboard are simply gone.
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I’ve normally found that enabling these causes more problems with stability…
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Trying out some settings…
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Experts Only!
The voltage options are not as robust for the memory or CPU as might be expected for a mainstream performer. The CPU voltages can be changed between 0.85V and 1.6V in 0.625V steps. The CPU FSB voltage may also be changed between 1.20V and 1.40V, and the nForce SPP between 1.20V and 1.50V in 0.05V steps. For Intel Core 2 chips, this may not be a significant issue for overclocking as they are fairly forgiving (as you will see later). However, the RAM voltage has been given the axe from the 680i’s 2.5V maximum to the 650i’s 2.2V maximum. As a result one would not be able to push the RAM speed to any great extent or with reasonable expectations for stability.
Overclocking
Knowing how our test-box CPU behaves, it was not too difficult to discover how simple it was to achieve a stable operation. As in the 680i review, I was able to overclock the CPU to 1333Mhz FSB @ 1.425V (note: the actual clock rate is 333Mhz, but the Intel FSB is “quad-pumped”) after disabling the spread spectrums.
The memory on the other hand was not going to be pushed far; our set of dominator 1142Mhz RAM sticks are actually able to be run in synchronous operation at 1333Mhz FSB, but that setting requires ~2.5V. Unfortunately for us, the system would run into memory errors when we tried to run the RAM at 1333Mhz (remember, that’s two times 667Mhz because it’s Double Data Rate RAM). Even lowering the RAM speed to 1142Mhz, the BIOS would only recognize 1110Mhz, and the system still would have trouble.
It seems the motherboard is not able to accurately attune to the frequency that one might desire (such as the rather odd 1142Mhz). However, it did just fine adhering to common frequencies (multiples of 100/133/166); I eventually found a nice stable operation at 1066Mhz memory speed @ 2.2V.
Note: Synchronous operation means that the quad-pumped CPU FSB is equal in frequency to the “doubled” frequency rate of the RAM. Although DDR2 RAM is marketed as the doubled or effective frequency, the BIOS options for the RAM are in terms of the true frequency. So for example, one might set 1333MHz as the CPU FSB. To be in synchronous operation with the RAM, the RAM frequency is entered as 667MHz instead of 1333MHz.
Asynchronous operation, while flexible, is not always ideal due to the communication between CPU and RAM. In this case, the motherboard has to use a CPU:RAM frequency divider to ensure proper operations. So, say that one runs the CPU FSB at 1333Mhz, but the RAM runs effectively at 1066Mhz. There is an exact 5:4 divider to make things operate relatively smoothly. But because the dividers are fixed, having strange FSB or RAM frequencies can be detrimental or ineffectual to performance even if running at higher frequencies; chances are your overall system performance won’t be enhanced much.