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Choosing the Best Mainboard to Overclock a Socket 754 CPU

The standard frequency of the Sempron 3100+ processor is 1.8GHz. Its multiplier is limited from above, like with any Athlon 64-like processor, i.e. you cannot increase it above the nominal value, 9x. The reduction of the multiplier is possible as necessary for Cool’n’Quiet technology, but it can’t help us during overclocking. Thus, the only way of overclocking the Sempron 3100+ is increasing the frequency of the clock generator above the standard 200 megahertz (some mainboard manufacturers still call it FSB frequency in the BIOS Setup). But in the majority of Socket 754 systems this very clock generator also forms other frequencies like those of the HyperTransport, AGP and PCI buses, and overclocking the Sempron 3100+ may lead to instability of the peripheral devices and chipset. For example, to overclock a Sempron 3100+ from 1.8GHz to 2.4GHz, you have to increase the clock generator frequency to 266MHz. In this case, the AGP frequency grows from 66MHz to 89MHz, and none of modern graphics cards would be operational at so high a clock rate. So, overclocking of Athlon 64 CPUs, and also of the Sempron 3100+, can’t be performed fully due to some problems with peripheral buses rather than to any limitations of the CPU itself. This problem was really serious until quite recently: there were no mainboards available to the masses that would clock the CPU and the AGP/PCI buses asynchronously. The situation is different now as NVIDIA has introduced its nForce3 250 chipset, capable of such asynchronous clocking. In other words, nForce3 250-based mainboards can overclock the CPU without raising the AGP/PCI frequencies.

So, we’ve got the answer: a Socket 754 mainboard on the NVIDIA nForce3 250 chipset is the best choice for overclocking the AMD Sempron 3100+ processor. Older mainboards on other chipsets are unlikely to allow getting the most from the processor.

Some things must be said about the memory frequency. The memory controller is integrated into the Sempron 3100+ core (like with Athlon 64 CPUs), and the memory frequency directly depends on the clock rate the processor works at. Higher CPU clock rates automatically lead to a higher memory clock rate. To form the memory frequency, the Sempron 3100+, normally clocked at 1.8GHz, offers the 1:9 divisor for DDR400, 1:11 for DDR333 and 1:13 for DDR266. There are no other divisors possible, so you have to think carefully before setting up the memory frequency at overclocking; otherwise, the memory chips may become unstable. The BIOS Setup of Socket 754 mainboards usually offers you to set up the memory frequency by choosing DDR400/DDR333/DDR266 (or 200/166/133MHz) in an appropriate menu. To understand what effective frequency the memory is working at in different overclocking situations, we offer you the following table:

So, it’s not so hard to set the right frequency for almost any DDR SDRAM modules, although this frequency changes along with the CPU clock rate. What you must do is choose an appropriate divisor in the BIOS Setup.

Now that you are warned about the possible troubles with choosing and configuring the overclocking platform, let’s proceed to the account of our overclocking experiments.

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