TRIGEM CW4D33E Operation Manual page 59

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 3 1/2-inch diskette, the write-protect device is a small
switch on the lower-right comer on the back, shown below. To
write-protect a 3 1/2-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 so the hole is covered.
3/14
Using Your Computer
Figure 3-7. 3 1/2 Diskette & Write-Protect SW