Acer Altos R910 - Manual (Page 84)

3 System upgrade 74
(4) Lift the cover from the memory board (D).
4 Locate the DIMM slots on the memory board.
5 Open the clips on the DIMM slot(s) (A).
6 Align (B) then insert the DIMM into the socket (C).
7 Press the holding clips inward to lock the DIMM in place (D).
Note: The DIMM slot is slotted to ensure proper installation. If
you insert a DIMM but it does not fit easily into the socket, you
may have inserted it incorrectly. Reverse the orientation of the
DIMM and insert it again.