Sony VGN-AR31E User Manual page 146

8 Slide the memory module into the memory module slot and push it in until it clicks into place.
!
If you use only one memory module, make sure to insert it to the slot that is closer to the back of your computer.
Do not touch any other components on the motherboard.
9 Replace the memory module compartment cover.
10 Tighten the screws on the bottom of the computer.
11 Reinstall the battery pack and turn on the computer.
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Upgrading Your VAIO Computer
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