Apple Mac Performa 640 series - Manual (Page 143)

Expansion cards are printed circuit boards that can be installed in your
computer to give it special capabilities, such as enhanced video, networking
and communications, and additional processing power.
You can install an expansion card by following the instructions that came
with the card, or by following the instructions in this appendix. However, be
sure to read this appendix for instructions that may be specific to your
computer.
If your computer comes with a Single Inline Memory Module (SIMM)
installed on the DOS-compatibility card, you can remove it or replace it with
a SIMM that has a higher memory capacity.
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Appendix B Installing an Expansion Card or
Memory for the PC Environment
Read this appendix for instructions
on installing an expansion card
in your computer or memory
for the PC environment.