Then a version of the Pascal programming language was adapted for the Apple II. This was a big breakthrough because Pascal is a powerful programming language, and the fact that it was available led to the development of lots of sophisticated applications for the Apple II. The only drawback to this breakthrough was that Pascal applications didn't use DOS 3.3. Pascal applications used their own operating system. (Now there's a version of the Pascal programming language that uses the ProDOS operating system, but the first version of Pascal for the Apple II required its own operating system.)

With Pascal on the scene, users had to keep track of whether the disks holding their documents were formatted for DOS 3.3 or for Pascal. If they tried to save a Pascal document on a DOS 3.3 disk, they got an error message, and vice versa.

Then came larger-capacity disks—3.5-inch disks and hard disks— capable of holding hundreds of documents instead of the dozens you could store on a 5.25-inch disk. The Pascal operating system was equipped to handle the larger storage devices, but DOS 3.3 couldn't. So DOS 3.3 was supplanted with a disk operating system that could take advantage of all that extra storage space.

The DOS 3.3 replacement was ProDOS, an acronym for Professional Disk Operating System. The most important feature of ProDOS, besides its ability to use all that extra storage space, is that it supports subdirectories. (It's the only one of the three Apple II disk operating systems that does; so if an application refers to subdirectories or pathnames, you know it's a ProDOS-based application program.)

64

Chapter 4: Saving Documents