Common Options : 0 to F (Hex numbers)

Details

These two options are slaved to the AGP 4X_Drive_Strength BIOS feature. If you set the AGP 4X Drive Strength to Auto, then the values you set using these two options won't have any effect. In order for these BIOS options to work, you need to set AGP 4X Drive Strength to Manual.

The AGP Drive Strength P Ctrl and N Ctrl options work hand-in-hand to determine the signal strength of the AGP bus. The AGP Drive Strength is represented by Hex values from 00 to FF. The higher the value, the stronger the signal.

As you can see, P Ctrl only has values from 0 to F. Therefore, it can only control the first part of the actual AGP Drive Strength value. The N Ctrl option also has values from 0 to F and thus, provides the remaining part of the actual AGP Drive Strength value. Confused? Here's the gist :-

The AGP Drive Strength is controlled by two Hex values (xx) ranging from 00 to FF (0 to 255 in decimal values). P Ctrl controls the first Hex value (Xx) while N Ctrl controls the second Hex value (xX). Together, they set the AGP Drive Strength value. For example, if you want to set an AGP Drive Strength of D4 (212), you will have to set P Ctrl to D and N Ctrl to 4.

On the reference motherboard, the default AGP Drive Strength was set as C5 (197). The default value will vary from motherboard to motherboard. But if you are using an AGP card based on the NVIDIA GeForce2 line of GPUs, then it's recommended that you set the AGP Driving Value to a higher value of EA (234). For other graphics cards, check with the manufacturer for the recommended AGP Driving Value.

Due to the nature of this BIOS option, it's possible to use it as an aid in overclocking the AGP bus. The AGP bus is sensitive to overclocking, especially in AGP4X mode and with sidebanding enabled. As such, a higher AGP Driving Value may be just what you need to overclock the AGP bus higher than normally possible. By raising the signal strength of the AGP bus, you can improve its stability at overclocked speeds.

But be very, very circumspect when you increase the AGP Drive Strength on an overclocked AGP bus as your AGP card may be irreversibly damaged in the process!

BTW, contrary to some reports, increasing the AGP Driving Value won't improve the performance of the AGP bus. It is not a performance enhancing option so you shouldn't increase the value unless you need to.