IBM ThinkPad T40 Hardware Maintenance Manual page 76

Removing and replacing a FRU
When installing: Insert the notched end of the DIMM into
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ThinkPad T40 Series (MT 2373, 2374, 2375, 2376)
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the socket. Press the DIMM firmly, and
pivot it until it snaps into the place.
Make sure that it is firmly fixed in the
slot and does not move easily.
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