Asus RS500-E6/PS4 - Manual (Page 26)

Chapter 2: Hardware setup 2-8
2.3.2 Memory configurations
You may install 512 MB, 1 GB, 2 GB, 4 GB and 8GB registered DIMMs or
Unbuffered DIMM with ECC / non- ECC into the DIMM sockets.
• Always install DIMMs with the same CAS latency. For optimum
compatibility, we recommend that you obtain memory modules from the
same vendor. Refer to the Qualified Vendors List on the ASUS web site.
• You may install varying memory sizes in Channel A, Channel B and
Channel C. The system maps the total size of the lower-sized channel for
the dual-channel or triple-channel configuration. Any excess memory from
the higher-sized channel is then mapped for single-channel operation.
• Due to the memory address limitation on 32-bit Windows OS, when you
install 4GB or more memory on the motherboard, the actual usable memory
for the OS can be about 3GB or less. For effective use of memory, we
recommend that you install a 64-bit Windows OS when having 4GB or more
memory installed on the motherboard.
• This motherboard does not support memory modules made up of 256 Mb
chips.