Epson 386/25 - Manual (Page 86)

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 it 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 S/t-inch diskette, cover the small,
rectangular notch (shown below) with an adhesive write-protect
tab. Write-protect tabs usually are included in a new package of
blank 5¼-inch diskettes.
To remove the write protection, peel off the write-protect tab.
3-16 Using Your Computer