TI-99/4A 90K

The TI-99/4A 90K format is a 5 1/4" single-sided, single-density floppy disk format used with Texas Instruments personal computers. Disks had 40 tracks (apparently a variant with 35 tracks also existed) and 9 sectors per track of 256 bytes each (apparently there could be variants with different numbers of sectors and different block sizes).

Links

 * Info on TI disk formats