AMD K10 - Phenom Overclocking Guide
Author: Zahn Funk
Editor: Shawn Knight
Date: 06-18-2008
Provided by: OCIA.net
Discuss: View Comments
CPU Speed

When you launch CPU-Z, the first tab, CPU, identifies the processor in your system, in this case the Phenom X4 9850. Here we can see the Name string, socket Package, die Technology and Core Voltage. It's also important to note that the Revision indicates this is a B3 chip. The Core Voltage and Clocks are updated in real time, so its not uncommon to see these numbers fluctuating slightly, especially under load.

Out of the four Clock values on this tab, Bus Speed is by far the most important. Just as with AMD's K8 processors, the Bus Speed value affects the frequency of every other major component in the system. With K8 and K10's integration of the memory controller into the processor, this is no longer a true bus speed. Often you will hear this value called the base or reference speed, and as the following formulas show, it does provide the main reference clock used for calculating all the other clock speeds.

Core Speed = Bus Speed X Multiplier / Divider
Northbridge = Bus Speed X Multiplier / Divider
Hypertransport = Bus Speed X Multiplier
Memory Speed = Bus Speed / DRAM Ratio

In your motherboard BIOS setup, Bus Speed is often referred to as CPU Frequency, which is really a misnomer. By default this value will be set to 200 Mhz, just as we saw in the CPU-Z utility. The other settings used to determine the CPU Core Speed are the Multiplier, CPU FID or Frequency ID, and the Divider, CPU DID or Divider ID. Those familiar with K8 overclocking will no doubt recognize the CPU FID but the Divider is something new to K10. Using the above settings as a reference, we can determine that the Phenom 9850 uses a 200 Bus Speed, multiplied by the FID of 12.5, and divided by the DID of 1. Thus 200 x 12.5 / 1 = 2500Mhz. Still with me? Good, now let's mix it up a bit.

Your particular BIOS may not be as straightforward to list the exact multipliers as FID options. Some may display a frequency instead, and some may only provide a field for you to manually type a hexadecimal value. The chart above should provide some assistance in determining what setting to use in case of the latter. Also there may be an "h" appended to the two digits indicating hex, as in 09h or just 9h. But in either case you can plainly see that we have far more choices for multipliers than the 4-16 or more available with K8 processors.

To further complicate the equation, there is now a DID that divides the CPU multiplier. By default this DID value is simply 1, which of course does not change the multiplier at all. However this can be set to 2, 4, 8 or even 16, and so not only do we have half-multipliers available as before with K8, but now quarter-multipliers or even smaller are possible by using a higher divider. To start out, I recommend keeping the DID value at 1 for simplicity sake. It can be implemented later if fine tuning of the CPU core speed is needed.

The VID or Voltage ID can be used to adjust the amount of voltage going to the core. This will become important later as we increase the Core Speed, as increases of the VID must be made in conjunction to maintain system stability.

Next let's take a look at something new for K10, the Northbridge frequency.

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