Asus P5RD2-VM - Manual (Page 66)

2-20 Chapter 2: BIOS setup
Memory Clock Mode [Manual]
Allows you to synchronize the Memory frequency with the CPU frequency.
Configuration options: [Auto] [Manual]
Refer to the DDR2 documentation before adjusting the memory voltage.
Setting a very high memory voltage may damage the memory module(s)!
OverClock Memory Clock [XXX]
Allows you to set the Memory frequency. Use the <+> and <-> keys to
adjust the Memory frequency. You can also type the desired CPU frequency
using the numeric keypad. The values range from 100 to 400.