Apple Macintosh PowerBook 1400 - Manual (Page 166)

m If a RAM card is already installed, slide the right edge of the card above
the card guide.
10 Lower the left side of the card so that its connector is aligned with the vertical connector
in the computer and gently push the card down until it is seated.
If the two connectors don’t join easily, detach the card and align the
connectors again. Forcing the connectors together could damage the card or
the socket.
A second RAM
card can be installed
above the card guide.
Card guide
166 Appendix C