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© Amit Singh. All Rights Reserved. Written in February 2004


First Bytes into an Apple

As 1975 came to an end, Steve Wozniak finished his prototype of what would become the first Apple computer. Wozniak's employer at that time, Hewlett-Packard, was not interested in his creation, so he requested, and was soon granted, a release of the technology. Apple was founded on April 1, 1976 by Steve Jobs, Steve Wozniak, and an Atari engineer named Ronald Wayne. The company's first product was Wozniak's computer, the Apple I.

Apple I

The Apple I was based on an 8-bit microprocessor, MOS Technology's 6502, running effectively at just below 1 MHz. The 6502 was similar to the more expensive 6800 from Motorola. The Intel 8080 was also around, but the 6502 was chosen primarily because it was cheap. The computer had a built-in video terminal, sockets for 8K bytes of onboard RAM, a keyboard interface, and a cassette board meant to work with regular cassette recorders. The "computer" was simply a motherboard: the user had to provide a case, an AC power source, an ASCII keyboard, and a display device.

The Apple I could be directly connected to a television with an RF modulator that resulted in a scrolling display with 24 lines of 40 characters each. It was introduced at a price of $666.66 that included 4K bytes of RAM and a tape of Apple BASIC.

Apple I
Apple I

The Apple I came with a firmware resident System Monitor, a program that can be thought of as its operating system. The monitor program was 256 bytes in size, and made use of the keyboard and display to present the user with a command line for viewing memory contents, typing and running programs, etc.

Compared to the UNIX general-purpose time-sharing system, which was in its Sixth Edition at that time, the Apple I's "operating system" doesn't sound like much. However, a computer running UNIX would have costed many thousands, perhaps even tens of thousands, of dollars then. The Apple I was an attempt to make computing affordable for hobbyists, and hopefully, for the masses.

Apple II

The Apple I would have a life span of less than a year, but its successor would live much longer. Wozniak had begun work on the Apple II which, although based on the same 6502 microprocessor, was introduced as an integrated computer: it came in a beige plastic case, with a built-in keyboard. Upon its release it was the first personal computer to display color graphics.

Various Apple II machines followed: the Apple II+, IIe, IIc, IIc+, IIe Enhanced, IIe Platinum, and finally the 16-bit IIgs, introduced in 1986. Many of these models had several revisions themselves.

A number of operating systems were created for the Apple II family.

Apple DOS

Shortly after the release of the Apple II in 1977, it was realized that a disk drive was imperative for the computer. Wozniak created a brilliant design for a floppy disk drive, the Disk II, and thus there was need for a disk operating system (DOS). Apple's first version of a DOS was released as Apple DOS 3.1 in July 1978.

Note that this was unrelated to Microsoft's popular MS-DOS. During a time when it was a luxury to have disk drives, and for an operating system to support them, many such "disk operating systems" had the term DOS in their names.

The first release was called 3.1 and not something like 1.0 because one of the implementers, Paul Laughton, incremented a revision counter x.y every time he recompiled the source code: it started with x = 0, y = 1, and every time y reached 9, x was incremented by 1. Apple DOS was beta tested as version 3.0.

Apple Pascal

The p-System from University of California at San Diego (UCSD) was very popular in the 1970's and the early 80's. It was a portable operating system, essentially a virtual machine, running p-code (akin to bytecode), with UCSD Pascal being the most popular programming language for it. Apple had a Pascal system for the Apple II derived from UCSD Pascal II.1, an implementation of the p-code architecture. Two UCSD students, Mark Allen and Richard Gleaves developed a 6502 interpreter in the summer of 1978. This later became the basis for Apple II Pascal released in 1979.

Apple Pascal lived as a product for five years.

Apple CP/M

Microsoft introduced a co-processor circuit board named Softcard in 1980. It was originally called the Microsoft Z-80 SoftCard, but Microsoft had to rename it to avoid a lawsuit from Zilog, the makers of the Z-80. The Softcard enabled the Apple II to run Z-80 programs based on the popular CP/M operating system that had a rich software library of programs, such as dBase and WordStar.

There were coprocessor cards other than Microsoft's, both for the Z-80 and other processors such as the Motorola 6809. The "Stellation Mill" 6809 card allowed OS-9, a real-time operating system to run on compatible Apple machines.

Apple SOS

The Apple III was introduced in 1980 as a computer for business users. It had a new operating system called SOS ("sophisticated" operating system, although it apparently was an acronym for "Sara's Operating System", after an engineer's daughter). Every SOS program loaded the operating system into memory as well. A SOS application disk consisted of a kernel (SOS.kernel), an interpreter (SOS.Interp), which could be the application itself, or something that the application used, and a set of drivers (SOS.Driver).

SOS evolved into Apple ProDOS.

Apple ProDOS

ProDOS, first released as version 1.0 in October 1983, was Apple's replacement for DOS 3.3, and was based on SOS. ProDOS provided better facilities for programming in BASIC, assembly language, and machine language, better interrupt handling, faster disk I/O with direct block access, and so on. It also had a relatively sophisticated hierarchical file system with features such as:

When the 16-bit Apple II came out, ProDOS (then at version 1.1.1) forked into ProDOS 8 and ProDOS 16 (for 8- and 16-bit processors, respectively).

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