IBM 5155 Manual To Operations page 246

Are you installing an IDM Math Coprocessor?
YES -
Continue with the next step.
NO - To install the IDM Personal Computer
Slimline Diskette Drive, go to step 28.
Note: Before you install the Math
Coprocessor, install the safety protector. The
Math Coprocessor can be identified by its
gold-colored pins.
19
Assemble the safety protector as shown in the
figure below. Insert slot A into slot B, then
insert slot C into slot D.
SlotC~
Slot B
\
Slot D
/
4-18 Option Installation