Epson 20 - Manual (Page 73)

On a 3½-inch diskette, the write-protect device is a small switch on
the lower-right corner 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.
write-protect switch
To remove the write protection, slide the switch toward the center of
the diskette until it clicks into position 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 and Reference diskettes that come with the Equity 386, and
use only the copies. Store your original MS-DOS diskettes in a safe
place away from your working diskettes. Back up your data diskettes
regularly, whenever you revise them, to keep them up-to-date, and
store them away from your originals.
4-16 Using the Equity 386