Epson 20 - Manual (Page 57)

Booting From the Hard Disk
Now you can boot your system (load MS-DOS) from drive C on your
hard disk. Be sure there is no diskette secured in drive A when you
turn on or reset your computer. Otherwise, your computer tries to
boot MS-DOS from the disk in drive A. If drive A is empty (or the
latch is up), MS-DOS is booted from drive C.
Turn off the computer, wait at least five seconds, and then turn it
back on. After the computer completes the power-on self test, the
screen displays the date prompt. Press Enter twice to accept the date
and time shown.
The C > prompt appears, indicating that the computer has
successfully loaded MS-DOS from your hard disk.
Preparing a Hard Disk for Use 3-13