This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
Copy II Plus is the best general purpose utility for copying disks and managing files on DOS 3.3 and ProDOS diskettes. Most of the Copy II Plus functions also work with disk images (e.g. .dsk files) on emulators; however, COPY DISK and FORMAT are important functions which do not work correctly with emulators. Good versions which handle both DOS 3.3 and ProDOS files are 7.x - 8.x. Note: Versions 9.x require at least an enhanced IIe and have a few notable bugs. Version 9.0's Catalog Sort option can mess up your directory. Neither version 9.0 nor 9.1 works correctly with the /RAM5 RAM disk. The best added capability of Version 9.x is being able to compare files. No version of Copy II Plus will copy files which include a resource part, usually called a "resource fork". In some cases the copy may seem to be successful; but, it will be a mess. Only some, relatively new, IIgs files include a resource fork. No DOS 3.3 files or files intended for access under ProDOS 8 have resource forks. The most versatile releases of the utility are, probably, Versions 7.1 and 7.2. They include the capability for creating disk images. The images are not compatible with popular emulators; but, they are a handy way to archive DOS 3.3 disks on a hard disk. For places to get Copy II Plus in ShrinkIt shrinked disk and emulator disk image files, refer to Q&A 007 above. By: tturner, Rubywand, Greg Buchner, Labelas Enoreth