This in-depth look at this copy protection system by [GloriousCow ... PC Option Board that would man-in-the-middle between the floppy disk drive and the CPU, intercepting data and render those ...

A DOS error message that means the floppy disk has been protected and data cannot be recorded on it. Either unprotect it or use another disk. See file protection ...

Additionally, the CRC was also altered to add another layer of protection ... with a standard IBM PC floppy disk controller; you need specialized hardware that can write different-sized sectors ...

A small, square cutout on the side of a 5.25" floppy disk used to prevent it from being written and erased. To enable the protection, the notch is covered with self-sticking tape. See file protection.

In fact, Shugart himself left IBM and transitioned to Memorex in 1972, helping the company deliver the first commercially available read-write floppy disk drive (the Memorex 650). A hallmark of ...