[acegopher]

I used an Xacto knife to create an extra notch in Commodore 64 5.25" disks back in the day so that I could take the single-sided disks and make them double-sided.

I would take one disk flipped over the other, mark the notch with a permanent marker, then cut out the outline. Most disks, like Elephant Memory, would work fine. You just flipped the disk over and inserted back into the 1541 to read the reverse side.

[nasalgoat]

I had a special square cutter tool specifically designed for this purpose. Just slot the disk in the tool, punch, done.

It helped when you were putting out hundreds of disks of pirated games on a regular basis.

[Luc]

I had a little switch to bypass the optical notch-detector on my 1541 drive.

I still think the single-sided disks were from the same production line as the double sided ones, and it was all market segmentation.

[honestcoyote]

I did the same. And disks were a bit expensive to a kid like me, so I'd even do the cut on various game disks I had, since many of them were single side only, and it was like getting a free disk.

[wayne_h]

"... flipped the disk over..."

They called them flippy disks...

[stuff4ben]

standard paper hole punch worked too, given enough hand strength :)