Your motherboard supports up to 24GB of RAM across 6 slots. Any combination of RAM modules (of equal size) that is less than or equal to 24GB in 6 slots will work. 6x4GB is just as good as 4x6GB or 2x12GB. As a rule, you should always have a even number of RAM modules (2, 4, 6, etc.) Using an odd number may result in some performance penalties (or may not work at all, depending on the motherboard.)
Both the OS and the software must be 64-bit versions. A 32 bit piece of software, even running on 64-bit Windows, can only use up to 4GB of memory; a 64-bit piece of software on 64-bit Windows effectively has no memory limits.
Edited by Andrew, 01 February 2013 - 02:22 PM.