Epson 3865X Plus - Manual (Page 85)

On a 3 diskette, the write-protect device is a small
switch on the back of the diskette in the lower right comer,
shown below. To write-protect a 3 ½-inch diskette, slide the
switch toward the edge of the diskette until it clicks into
position, exposing a hole in the comer.
write-protect switch
To remove the write protection, slide the switch toward the
center of the diskette until it clicks into position and the hole is
covered.
Using a Single Diskette Drive System
MS-DOS expects the computer to have at least two diskette
drives and displays prompts and messages accordingly. Usually,
MS-DOS recognizes the first diskette drive (the top drive on
your computer) as A and a second diskette drive as B. If you
have only one diskette drive, MS-DOS can treat it as both A
and B when you need to perform operations that normally
require two diskette drives.
3-18 Using Your Computer