Abit AX5 Instruction Booklet page 41

Installing the Mainboard
Computer
Knowledge
The voltage for the 72pin SIMM is +5V, and the 168pin DIMM
is +3V, according the specification, it strongly recommend that
should not mix both kinds of memory module, it may cause the
total amount of memory size is different with the memory that
plug-in when install mix both kinds of memory module.
may be the following reasons :
1. The DRAM' s specification is different, can be mixed.
2. The DIMM and SIMM using the same RAS signal, and
sharing and it limit by the chipset design.
2-25
It