In K8 and K10 architecture, the motherboard FSB or Front Side Bus is no more, this function is now handled by the processor. This can be referred to as the Northbridge or IMC, Integrated Memory Controller. With K8 processors, the Northbridge runs at the same frequency as the Core Speed by default and cannot be changed. Now with K10, this value is typically less than the Core Speed and can be individually adjusted. The current operating speed of the Northbridge can be found on the Memory tab in CPU-Z, labeled NB Frequency.

Northbridge = Bus Speed X Multiplier / Divider

Remember that the Bus Speed is also used in determining NB Frequency.


Just as with the CPU Frequency, NB Frequency is controlled through use of a FID and DID. And also like the CPU FID value, the options you have in your BIOS will vary. Some may show a frequency while others use a hex setting. Some, like the AMI version shown above, do not even offer a NB DID. But in others you may have the option to change the default 1 to a 2. In the case of the Phenom 9850, the NB Frequency is 200 x 10 / 1 = 2000 Mhz. It is important to note that the NB FID, while potentially represented as a frequency, is not a fixed value. Setting this to 2000 Mhz does not mean it remains at 2000 Mhz if the reference clock is changed. 2000 Mhz in this case simply means it is using a 10x multiplier.


Here is a chart to help sort out the various possible settings for NB FID. As with adjusting CPU frequency, increasing the NB frequency over stock may require some additional voltage to keep the system stable. This can be set using the NB VID value.

Up next, the Hypertransport bus.