This package contains reverse-engineered source code for the System Software and Disk Operating System Software of the Apple ][ series computers from Apple, Inc.

The source code is intended to be processed by m4 and assembled by xa65 Assembler.

Apple ][ Library

(A private archives not affiliated with Apple, Inc.)

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Apple ][ System and DOS: apple2sys.tar.gz (prerequisites: a2catalog.tar.gz xa)

Apple ][ DOS Master Disks: apple2sysmas.tar.gz

Apple ][ System Software

The Apple ][ and Apple ][ plus computers came with System Software in their ROM chips from the factory. The System Software is commonly called “firmware,” or simply “ROMs.”

The first Apple ][ had the “Monitor” system firmware, as well as the “Integer BASIC” programming language interpreter and command line shell, and a few other miscellaneous features, such as “Sweet-16” and the Mini Assembler. The Apple ][ plus had an updated Monitor, sometimes known as the “Autostart Monitor,” and replaced Integer BASIC and the misc. routines with a new floating-point BASIC, called “Applesoft BASIC,” which was written by Microsoft (in its earliest days).

Apple ][ Disk Operating System Software

The Apple ][ Disk Operating System Software is commonly known as “DOS 3.3”. This software is on most Apple ][ floppy disks, and is loaded into the computer from the floppy during the “boot” process. The Disk ][ Controller peripheral card contains some firmware that begins the boot process. The rest of DOS is stored on the floppy disk. There were different versions of DOS released by Apple, in two incompatible forms: the earlier with 13 sectors per disk track, and the later, most common, format, with 16 sectors per track.


Breakout is the game that started it all. A version of Breakout, in Integer BASIC, from the earliest Apple ][ reference manual, with line-by-line annotations, is available.

Recovery Effort

These pieces of software are not easily available today, in source or binary form. The System Software can only be obtained in binary form, and only by purchasing an actual Apple ][ through private sale (or auction). Some of the source code was published (in printed form only) in various reference manuals from Apple, which are also hard to come by. As for the DOS software, version 3.3 is the most common, but is only available in binary form, and only through private channels. The older versions of DOS are almost impossible to find. And none of the DOS source code was ever made available officially.

After years of tireless effort, we have been able to completely recreate all of the System Software and DOS Software in source form. The source is (highly commented) 6502 assembly language, intended for the xa65 Assembler, although porting it to other 6502 assemblers should not be too difficult. Included in the recovery effort was all System Software for the Apple ][ and ][ plus, including the Monitor and both BASIC interpreters. Also included were the Disk Operating System Software versions 3.1, 3.2, 3.2.1, and the three different releases of version 3.3. The (known) official “System Master” disks were recovered as well. Also included were the (yet) older versions of Monitor and Integer BASIC that were provided for the Apple I (one).

More details on specific versions are available in source code comments, and in various README files that also come with the source distributions. As stated above, these works are provided for private study, scholarship, or research only, and are (or may be) copyright by Apple, Inc., or others.

Source Code Repository