Overclocking Your K8 Processor
There are a few differences when overclocking K8 processors like our Athlon 64 X2 5400+. First, ACC can not be used for K8 processors, so the option is missing from the BIOS and grayed out in AOD. Second, there is no adjustment of northbridge speed to worry about, so references to northbridge speed or frequency will now be missing in AOD and CPU-Z.
The third difference and biggest concern for our easy Black Edition multiplier overclocking has to do with the memory frequency. Rather than being based on a reference clock and multiplier, like we have seen so far with the K10 chips, the memory speed is based off of the CPU speed. This means that when we increase the multiplier we also change the memory frequency.
Official support ranges up to DDR2-800, so the CPU speed is divided by a value to keep the memory less than or equal to 400 MHz (DDR2-800). This means that chips with even multipliers can run DDR2-800, while chips with odd or half multipliers will run the memory slower than 400 MHz.
Our X2 5400+ uses a 14x multiplier, resulting in a core speed of 2,800 MHz. With our memory set to DDR2-800 in the BIOS, the memory frequency is based on the CPU speed divided by 7 (half the multiplier) and thus runs at 400 MHz (DDR2-800). Bumping up the multiplier to 14.5x would result in 2,900 MHz, and since the memory cannot run at over 400 MHz, the memory divider used is raised to 8 (the next highest whole number), resulting in a memory frequency of only 363 MHz. Raising the CPU multiplier in half increments shows a trend, as 8 remains the memory divider for a 15x, 15.5x, and 16x multiplier. Of course, 16x is an even multiplier, resulting in a memory frequency of 400 MHz again:
However, notice that the memory frequency can still be overclocked by raising the reference clock:
Keeping these differences in mind, you should be able to overclock a K8 processor following the same steps that we have outlined. Also, it is important to note that the HyperTransport link speed is much lower with K8 processors, so do not expect to have stability with a dramatically overclocked HyperTransport link.
