Software
A major limitation of the Apple II and DOS 3.3 was the way it addressed resources, which made it highly desirable for peripherals to be installed in standardized locations (slot 5 and 6 reserved for storage devices, slot 2 reserved for serial communication interfaces, etc.) This forced the user to identify a peripheral by its physical location, such as PR#6, CATALOG,D1, and so on. The Apple III introduced an advanced operating system called Apple SOS, pronounced "apple sauce". Its ability to address resources by name instead of a physical location allowed the Apple III to be more scalable. Apple SOS also allowed the full capacity of a storage device to be used as a single volume, such as the Apple ProFile hard disk drive. Also, Apple SOS supported a hierarchical file system (HFS). Some of the features and code base of Apple SOS made their way into the Apple II's ProDOS and GS/OS operating systems, as well as Lisa 7/7 and Macintosh system software.
The Apple III also introduced a new BASIC interpreter called Apple III Business BASIC, and later an implementation of UCSD Pascal for more structured programming.
Originally intended as a direct replacement to the Apple II series, it was designed for backwards-compatibility of Apple II software in order to migrate users over. However, since Apple did not want to encourage continued development of the II platform, Apple II compatibility on the Apple III existed only in a special "Apple II Mode" which was limited in its capabilities to the emulation of a basic 48 KB Apple II+ configuration, with no access to the III's advanced features such as its larger memory, a restriction which actually required custom chips to enforce. Since many business-oriented Apple II programs started requiring at least 64 KB of RAM (i.e. an 48 KB Apple II with an added 16 KB "language card") around the time the III was released, they were incompatible with the III, preventing some users from switching over.
The Apple III had a System Utilities program, which allowed system reconfiguration and file manipulation. Another program, Selector III, was designed to integrate with the System Utilities program and launch various applications. The program was developed by ON THREE, a large Apple III user group. Another company, Quark Software, developed a competing product, Catalyst, the cruder interface of which was offset by program-switching capabilities and support for copy-protection, which enabled companies to license users to run programs from a hard disk without worrying that their software might be backed up or copied without permission. When Apple decided to bundle Catalyst with its new ProFile hard disk, Quark celebrated, but ON THREE continued to market and sell Selector III through their monthly magazine. Selector III remained commercially available and supported long after Quark discontinued its Apple III product line.
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