iPDS floppy format

80 tracks

track 0/0 128 bytes 16 sectors SD G1:16 G2:25
other tracks 256 bytes 16 sectors DD G1:32 G2:50

interleave

1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15, 4, 8, 12, 16