This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
Most emulator programs have no problem using .po, .do, or .dsk disk images. So, the usual reason for wishing to change ordering is to go from .po (ProDOS order) to .dsk (typically, DOS 3.3 order) to permit transferring the image to your Apple II via ADT. In a few cases, it may be useful to go from DOS 3.3 order to ProDOS order, too. Since a disk copy done on an emulator (like AppleWin) adjusts ordering to match the target, doing a disk copy from, for example, a .po image to a .dsk image (in DOS 3.3 order) is a simple way to do a conversion*. A good emulator choice for Windows users is AppleWin. A good disk copier program is Disk Muncher-- it is included on the TNILUTIL.DSK available from Ground and GSWV. An easy way to check ordering of a bootable .po or .do disk image is to boot it under AppleWin. If it boots correctly, the ordering is as claimed-- .do = DOS 3.3 order and .po = ProDOS order. For a bootable .dsk image, you can change the suffix to ".do" or ".po" and boot it to check that it is really in the order you expect. *Note: AppleWin, evidently, checks the ordering of a .dsk image used as a target for copying. It does not check actual ordering of .po or .do images. So, for example, if the target image has the ".po" suffix, the copy to the image will be in ProDOS order. Some emulators may work differently. By: David Kopper, Dan DeMaggio, Boris Guenter, Nathan Mates, Phil Abro, Rubywand, Labelas Enoreth, Tony Turner