A:Please refer the description Q4 of Q&A-20.
https://www.asrock.com/support/QA/TSDQA-20.pdf
This limitation applies to most chipsets & Windows^® XP 32-bit version operating system.
If you want to get 4GB memory for your system, below two conditions must be required:
1. The memory controller which supports memory hole(memory remap) functionality is used. The latest chipsets like Intel^® new chipset, or other chipsets and AMD^® K8 CPU architecture can support the memory hole(memory remap) function.
2. Windows^® XP Pro X64 Ed. (64-bit) or other OS which can address more than 4GB memory.
http://www.intel.com/support/motherboards/server/sb/cs-016594.htm