Epson 486SX - Manual (Page 127)

Set the jumpers according to the table below.
Hard
disk drive jumper settings
X = jumper installed
- = no jumper installed
To move a jumper from one position to the other, use your
fingers, needle-nose pliers, or tweezers to pull it off its pins and
gently move it to the other position. Be careful not to drop the
jumper or damage the pins as you install it.
If you are going to use only one hard disk drive, make sure the
jumper is set in position DS.
If you’ll be using two hard disk drives, install two jumpers on
the master drive in positions SP and DS. Do not install any
jumpers on the slave drive.
To install or remove a drive in the internal drive bay, see
page 7-14.
To install or remove a drive in the external drive bay, see the
next section.
Installing and Removing Drives 7-5