Asus P4PE - Manual (Page 32)

2-6 Chapter 2: Hardware information
3. Position the CPU above the socket such that its marked corner
matches the base of the socket lever.
4. Carefully insert the CPU into the socket until it fits in place.
The CPU fits only in one correct orientation. DO NOT force the CPU
into the socket to prevent bending the pins and damaging the CPU!
5. When the CPU is in place, push down the socket lever to secure the
CPU. The lever clicks on the side tab to indicate that it is locked.
Gold Mark