IBM RT PC Options Installation page 58

2-14 Options Installation
Warning: Follow all instructions under "Removing the Covers
from the System Units" on page 1-4 before installing the drive in
position C.
1. Remove the cooling fan assembly. Refer to "Cooling Fan
Removal" on page 2-5.
2. Use the following illustration to identify which drive you are
installing.
Note: IBM 310 megabyte fixed-disk drives may look like either
of the bottom two examples below.