System Memory; Recommended Memory Configurations - Asus SABERTOOTH 990FX User Manual

2.2.3 System memory
The motherboard comes with four Double Data Rate 3 (DDR3) Dual Inline Memory Modules
(DIMM) slots.
A DDR3 module is notched differently from a DDR or DDR2 module. DO NOT install a DDR
or DDR2 memory module to the DDR3 slot.

Recommended memory configurations

ASUS SABERTOOTH 990FX 2-5