>>11812782
It's a 3 inch disk format developed by Panasonic. Several computers used it initially but it quickly lost the format war to Sony's famous 3.5 inch floppy. Amstrad then bought nearly the entire world's supply of disks for cheap and every software publisher had to buy them from Amstrad, similar to Nintendo manufacturing cartridges for NES publishers. In fact some publishers just slapped their cheaply printed labels on disk, leaving stock red Amsoft-branded disk labels visible through.