Epson Equity 286 PLUS - Manual (Page 192)

8. Both the diskette drive and hard disk drive sockets are
located on the main system board on the left side of the
subassembly, as shown below.
diskette drive
socket
hard disk drive
socket
subassembly
Both sockets have a notch on one side. The hard disk drive
socket is also a bit longer than the diskette drive socket.
Installing and Removing Disk Drives B-53