Apple PowerBook (3400 series) - Manual (Page 155)

You can purchase a RAM card to augment your PowerBook’s operation.
Note: You should attempt to install a RAM card only if you are comfortable
working with electronic equipment. You should read all of the following
instructions before you begin. If the procedure sounds like something you
don’t want to do yourself, any Apple-authorized service provider can install
the card for you (for a service charge).
WARNING If you attempt to install a RAM card yourself, any damage
you may cause to your equipment will not be covered by the limited
warranty on your computer. See an Apple-authorized dealer or
service provider for additional information about this or any other
warranty question.
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Appendix C Installing a Macintosh PowerBook
RAM Expansion Card
Refer to this appendix for instructions
on installing a Macintosh PowerBook
RAM expansion card.