IBM RT PC Options Installation page 117

TNL SN20-9864 (May 1987) to 75X0217
Installing Processor Options
CAUTION
Turn off the power on the system unit and unplug the power cable from
the electrical outlet.
If you have not removed the covers, see "Removing the Covers From the
System Units" on page 1-4.
You may carefully lay the IBM 6150 system unit on its side to install
adapters, if you need to do so.
Refer to "General Instructions" on page 3-4 when necessary for
information on installing adapters.
4-4 Options Installation