IBM RT PC Options Installation page 30

TNL SN20-9864 (May 1987) to 75X0217
Identifying Adapter Positions
Look at the adapter slots on the system diagram you unfolded earlier. In
the IBM 6150, notice that adapter slots 2, 4, 5, 7, and 8 have two tab slots,
while adapter slots 3 and 6 have only one tab slot. If an adapter has one
tab, try to put it in adapter slot 3 or 6, saving the positions with two slots
for adapters with two tabs.
In the mM 6151, notice that slots 2, 3, 4, and 5 have two tab slots, while
slot 1 has only one tab slot. If an adapter has only one tab, try to put it in
adapter slot 1, saving the slots with two tabs for adapters with two tabs.
The following illustration shows the tab positions of the adapters you can
install in the system units. The adapters all have one of the following basic
forms:
Section 1. Getting Started 1-15