Asus P4S333 - Manual (Page 34)

2-12 Chapter 2: Hardware information
3. Firmly insert the DIMM into the socket until the retaining clips snap
back in place and the DIMM is properly seated.
Locked Retaining Clip
2.5.3 Installing a DIMM
Make sure to unplug the power supply before adding or removing
DIMMs or other system components. Failure to do so may cause
severe damage to both the motherboard and the components.
Follow these steps to install a DIMM.
1. Unlock a DIMM socket by pressing the retaining clips outward.
2. Align a DIMM on the socket such that the notch on the DIMM matches
the break on the socket.
Unlocked Retaining Clip