The "disk notcher" was a tool used to take advantage of BOTH sides of a 5 1/4 inch floppy disk. Manufacturers of the disks provided one notch that allowed the disk drive (I had/have 2 1541s) to access the information stored on the disk. Some creative person found that by adding a notch in the other side of the disk the user could then flip the disk over and use the other side. The 1541 was part of the Commodore 64 family.
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