Apple II disk images formats: .PO .DO and .IMG

REF: http://www.applelogic.org/TheAppleIIEGettingStarted.html

ProDOS-Order (.PO)

.PO disks contain logical disk bytes, i.e. blocks of 256 bytes each sorted by their logical block number. Since they are only used for dumping floppies, .PO images always have 560 blocks originating from 35 tracks of 16 sectors each. You can use the following translation table to find out about a sector’s physical block number:
Block: 0 1 2 3 4 5 6 7 8 9 A B C D E F Position: 0 8 1 9 2 A 3 B 4 C 5 D 6 E 7 F
This table mirrors ProDOS’ hard-coded interleaving. It is different from the one found on DOS 3.3 disks.

DOS-Order (.DO)

.DO disks contain logical disk bytes, i.e. blocks of 256 bytes each sorted by their logical block number. Since they are only used for dumping floppies, .DO images always have 560 blocks originating from 35 tracks of 16 sectors each. You can use the following translation table to find out about a sector’s physical block number:
Block: 0 1 2 3 4 5 6 7 8 9 A B C D E F Position: 0 7 E 6 D 5 C 4 B 3 A 2 9 1 8 F
This table mirrors DOS 3.3′ hard-coded interleaving. It is different from the one found on ProDOS disks.

NIB

.NIB images are copies of a disk’s nibblized disk bytes. Since they are pure copies without having gone through any sort of decoding, they work equally well for both DOS and ProDOS disks.
.NIB images are made up of 35 tracks. Each track has $1A00 (6656) bytes. There’s no header structure. The first disk byte of track 0 starts at file offset +0, the first byte of track 1 at file offset +$1A00, and so on