Epson Apex 20020 - Manual (Page 67)

Note
Some program diskettes, such as your MS-DOS diskettes,
have no notch so they are permanently write-protected. This
protects them from being accidentally erased or altered.
On a 3½-inch diskette, the write-protect device is a small
switch on the lower-right comer on the back, shown below. To
write-protect a 3½-inch diskette, slide the switch toward the
edge of the diskette until it clicks into position, exposing a hole
in the corner.
To remove the write protection, slide the switch toward the
center of the diskette so the hole is covered.
Making Backup Copies
It is important to make copies of all your data and system
diskettes. Copy all diskettes that contain programs, such as the
original MS-DOS diskettes that come with your computer, and
use only the copies. Store your original MS-DOS diskettes in a
safe place away from your working copies. Back up your data
diskettes regularly, whenever you revise them, to keep them
up-to-date, and store them away from your originals.
Using Your Computer 3-15