Asus P4PE - Manual (Page 37)

ASUS P4PE motherboard user guide 2-11
2.5.2 Memory configurations
You may install any DDR DIMMs with 64MB, 128MB, 256MB, 512MB, and
1GB densities into the DIMM sockets.
1. DDR DIMM sockets 2 and 3 share the same rows, so if you install
a double-sided DIMM into DIMM2 socket, you must leave DIMM3
socket empty.
2. You may install single-sided DIMMs into DIMM2 and DIMM3
sockets at the same time but neither one can be x16 DDR module.
3. Double-sided x16 DDR DIMMs are not supported on this
motherboard.
Use only the following combinations to install DDR DIMMs. Otherwise,
the system may not boot up.
DDR DIMM1 DDR DIMM2 DDR DIMM3
(Rows 0&1) (Rows 2&3) (Rows 3&2)
SS/DS DS None
SS/DS SS SS
* SS - Single-sided DIMM
DS - Double-sided DIMM