Epson 20 - Manual (Page 72)

Write-protecting Diskettes
You can write-protect a diskette to prevent its data from being altered.
When a diskette is write-protected, you can read it and copy data
from it, but you cannot store new data on the diskette or delete any
files it contains. If you try to change data stored on a write-protected
diskette, MS-DOS displays an error message.
To write-protect a 5¼-inch diskette, cover the small, rectangular
notch (shown below) with an adhesive write-protect tab. Write-
protect tabs usually come with new 5¼-inch diskettes when you buy
them.
\
write-protect
notch
To remove the write protection, peel off the write-protect tab.
Using the Equity 386 4-15