Epson EQUITY 386/33 PLUS - Manual (Page 25)

On a 3½-inch diskette, the write-protect device is a small
switch on the back of the diskette in the lower right corner,
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 comer.
To remove the write protection, slide the switch toward the
center of the diskette until it clicks into position and the hole is
covered.
Note
Some program diskettes have no notch or switch so they are
permanently write-protected. This protects them from being
accidentally erased or altered.
Using Your Computer 1-15