Asus M3N-HD - Manual (Page 38)

2-12 Chapter 2: Hardware information
This motherboard can support 4 GB physical memory on the operating systems
listed below. You may install a maximum of 2 GB DIMMs on each slot.
64-bit
Windows ® XP Professional x64 Edition
Windows ® Vista x64 Edition
Always use identical DDR2 DIMM pairs for dual channel mode. For optimum
compatibility, it is recommended that you obtain memory modules from the
same vendor. Visit the ASUS website (www.asus.com) for the latest Qualified
Vendors list.
Important notice on installing Windows ® XP 32-bit version
If you install Windows ® 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 ® 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.
Visit the ASUS FAQ site for further
explanation:
http://support.asus.com/faq/faq.
aspx?SLanguage=en-us
Under General Search, make the
selections as shown, then click Search. Click the article titled “4GB memory
installed but less memory size detected.”
You also may check the URLs below for third party comments on this issue:
http://dlsvr01.asus.com/pub/ASUS/mb/4GB_Rev1.pdf
http://www.intel.com/support/motherboards/server/sb/cs-016594.htm