IBM 3740 format
The IBM 3740 format of 8" floppy disks was used in the 1970s IBM 3740 data entry system, which replaced keypunch systems that stored data on punched cards.
The disk format was single-sided, single-density, and had 73 tracks with 26 sectors storing 128 bytes per sector. The total capacity was 237.25 KB. FM encoding was used.
Although 8-inch floppies were extremely rare on IBM PCs, the physical format of IBM PC 5.25 inch and 3.5 inch floppies is directly descended from that of the IBM 3740, with various enhancements – as well as the physical shrink in the disk size, there was also the switch to double-sided, double density (MFM encoding) instead of single density (FM encoding), and support for sectors larger than 128 bytes (most IBM PC floppy controllers support any power-of-2 sector size between 128 and 4096, but the vast majority of floppies were formatted with 512 byte sectors.) This includes inheriting various obscure and rarely used IBM 3740 features, such as "deleted sectors".
