IBM RT PC Options Installation page 87

• If you are installing an E or 310 megabyte fixed-disk drive,
connect C-E1 (C-CDE is already connected) to the IBM RT PC
Extended ESDI Magnetic Media Adapter as shown.
12. Install the adapter:
• If you are installing an R40 or R70 fixed-disk drive, install
the second drive adapter in adapter slot 2. If you need
instructions for installing the adapter, see "Installing
Adapters" on page 3-7.
Section 2. Removing and Installing Drives in IBM 6150 2-43