Apple IIgs - Manual (Page 22)

Page 22 of 84 II gs
Printed: Thursday, July 25, 2002 12:14:50 PM
assumes you want to save it on the disk in the drive you last accessed.
Disk Operating Systems
When you tell your application to save a document on a disk, it hands the job over to a
subcontractor called the disk operating system.
The disk operating system is a set of programs on every application program disk that handles
the transportation of documents between the memory of the computer and disks.
The only reason you need to be aware of the disk operating system is that there are three
varieties;ProDOS, Pascal, and DOS 3.3;and each variety requires that disks be formatted in a
particular way. If your application uses ProDOS (that is, if the application is ProDOS-based),
documents created with that application can be stored only on ProDOS-formatted disks. If your
application program is Pascal-based, documents created with that application can be stored only
on Pascal-formatted disks.
If formatting is handled by the application, you don't need to know what that application's
disk operating system is;the application knows and will format disks the way it needs them to
be formatted.
If formatting isn't handled by your application, you'll use the System Disk and you'll be asked
whether you want the disk formatted for ProDOS or Pascal.
How do you know what operating system your application uses so you know how to answer the
question? You can usually find out by looking at the label of the application program disk or
by using the Catalog a Disk command on the System Disk.
If there is no operating system shown on the label, see if the application's operating system
is mentioned in the application program's manual. (It will most likely be mentioned in the
chapter that discusses how to save documents on disks.)
If you want to know why there are three disk operating systems for the Apple II, and more about
them, read on.
Apple II Disk Operating Systems
In the beginning, there were only 5.25-inch disks and one system for saving information on
them. The system was called DOS, an acronym for Disk Operating System. (Over the years, DOS was
improved, and version numbers were tacked on to distinguish one version from the next. The last
and best version was DOS 3.3.)
The first applications written for the Apple II were written either in assembly language (a
programming language only slightly removed from the language of 0's and 1's that the Apple II
speaks fluently) or in BASIC (a programming language that uses English-like words to tell the
computer what to do). Both assembly-language programs and BASIC programs used the DOS 3.3
system for formatting disks and for saving and retrieving documents, so users didn't have to
know what kind of program they were using.
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 program-ming
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