Dell Vostro 420 (Late 2008) - Manual (Page 105)

Memory Module(s)
105
1 Align the notch on the bottom of the module with the crossbar in the
connector.
.
NOTICE:
To avoid damage to the memory module, press the module straight down
into the connector while you apply equal force to each end of the module.
2 Insert the module into the connector until the module snaps into position.
If you insert the module correctly, the securing clips snap into the cutouts
at each end of the module.
3 Follow the procedure in "After Working on Your Computer" on page 45.
4 When the message appears stating that memory size has changed, press
to continue.
5 Log on to your computer.
1 cutouts (2) 2 memory module
3 notch 4 crossbar
3
2
1
4