Epson EQUITY 3865X/20 PLUS - Manual (Page 149)

A master drive is the drive on which you’ll install the operating
system that the computer loads into its memory each time you
turn it on. You can run application programs and store data on
both the master drive and the slave drive, but the master drive
must contain the operating system.
Follow the instructions in the next section to change the jumper
settings on both of your hard disk drives.
Changing the Jumper Settings
The hard disk drive jumpers are located
board, near the large cable connector.
on the drive’s circuit
ACT
large cable
connector
The jumpers on your drive may be in a slightly different
location, but you set them the same way.
Installing and Removing Disk Drives 7-5