Asus M2A-MX - Manual (Page 26)

1-14 Chapter 1: Product introduction
• When using only one memory module, start installing the DDR2 DIMM from
slot DIMM_A1 or DIMM_B1 for better overclocking capability.
• Always use identical DDR2 DIMM pairs for dual channel mode. For
optimum compatibility, we recommend that you obtain memory modules
from the same vendor.
Important notice on installing Windows ® Vista / XP 32-bit version
If you install Windows ® Vista / XP 32-bit version Operating System (OS), the
limitation of this OS version is that it may reserve a certain amount of memory
space for system devices. We recommend that you install less than 3 GB
system memory if you would like to work under Windows ® Vista / XP 32-bit
version OS. The excess memory installation will not cause any usage problem,
but it will not give users the benefit of manipulating this excess memory space.
64-bit
Windows ® XP Professional x64 Edition
Windows ® Vista x64 Edition
The motherboard can support 4 GB physical memory on the operating system
listed below. You may install a maximum of 2 GB DIMMs on each slot.