This article explores Formaster Corporation’s Copy-Lock protection technology used on King’s Quest I for IBM PC. The protection technique involves setting bad CRC values in sectors, misleading sector IDs, and manipulating sector sizes to thwart unauthorized duplication and use. By implementing Read Track commands instead of Read Data, Copy-Lock evades simple sector-based copying methods. The protection scheme struggled with speed variations and lacked compatibility with DMA-less PCs like the PCjr. and early Tandy 1000 models. The necessity for DMA mode for proper operation is evident, while the CPU speed sensitivity raised challenges for faster machines.
https://martypc.blogspot.com/2024/08/pc-floppy-copy-protection-formaster.html