Apple Pascal refers to an operating system for the Apple II family of computers released in August of 1979 between the Apple DOS 3.2 and 3.3 versions. The system was included as part of a software/hardware package adding support for the Pascal language to the Apple II. It added a number of features that would later be incorporated into the 3.3 version, as well as others that would not be seen again until the introduction of ProDOS.

The biggest changes were to the disk format and file storage methods, as Apple Pascal was designed to take advantage of 140K 5.25" floppy disks. Instead of dividing the disk into 256-byte sectors as with DOS 3.2, Apple Pascal divided it into "blocks" of 512 bytes each, each block thus contained two sectors. This made for a different method for saving and retrieving files. Under Apple DOS, files were saved to any available sector that the OS could find, regardless of location. This caused larger files to become fragmented and slowed down access to the disk when loading and saving. Apple Pascal attempted to rectify this by saving only to consecutive blocks on the disk.

Drawbacks included the new limitations on the naming of files. While Apple DOS allowed filenames up to thirty characters long and any ASCII character could be used, Apple Pascal dropped the length to fifteen characters and allowed only letters, numbers and periods to be used. This was done to create a cleaner look to the disk's catalog, or file listing, as shorter filenames would minimize the "wrap-around" on the screen. As most Apple displays at the time were only 40 characters wide, the filename limitations were not seen as that great a drawback.

The consecutive file saving method also created some problems. Deleted filespace could not be used if it was not at the "end" of the disk (after the most recently-saved file). A utility, charmingly called Krunch, was included in the package to "clean up" the disk by moving files until they were all consecutively stored again.

The advantages though, were significant, aside from just the increase in disk access speed. Apple Pascal increased the number of supported file types from the original eight by introducing a two-byte code to indicate type. A timestamp feature was also added, indicating the date and time of a file's creation or last modification. This data would then be shown on a line with the filename by the CATalog command. Previously only a file's name, basic type, and size would be shown. Strangely enough, the timestamp feature was not made a part of the later DOS 3.3.

Disks could also be named for the first time. Under Apple DOS, disks could only be given a volume number, but Apple Pascal disk volume names could be up to seven characters in length.

The Apple Pascal software package also included disk maintenance utilities, the Pascal compiler (set to the UCSD standard), and a decently-featured assembler to complement the Apple II's built-in "monitor" assembler.