The Computer History Museum has scored something of a coup, publishing – with Cupertino's permission – the source code for the Apple II's DOS, version 3.1.
The archeological code, posted here, is the whole 4,000-plus – that's thousands of lines of code, not millions in a misprint – complete with comments like “if it ain't 3 don't reloc”.
As Computer History Museum notes on its release page, the DOS – which included a file manager, a BASIC interface, and various utilities – was written for US$13,000 (a little over three dollars a line) by Paul Laughton, a contractor for Shepardson Microsystems.
The code was written between April and June 1978 – a fair achievement for a brand new DOS – and by October, according to meeting minutes posted by the Museum, Apple and Shepardson were already working through the bug fixes and discussing the documentation. This kind of discussion still rings true to anyone looking at software development.
For example, there's this exchange involving Laughton and Randy Wigginton (employee number six, and creator of MacWrite):
“Paul has received questions directly regarding our DOS. Evidently he has been in computer stores, etc. when someone was asking questions about the Apple DOS. He also was surprised that we were shipping documentation on the Read/Write a track and sector routine. He felt that documentation on interfacing to the file manager portion of the DOS was more useful. Randy pointed out that documentation does not exist on the file manager.”
Another amusing insight covers “bug #1”:
“There was some controversy as to whether bug #1 was or was not actually specified in the original spec. Paul felt that bug #1 involved some major rework, and was a result of not having a written spec on the DOS.”
As the Museum notes, the Apple II couldn't compile anything, so Laughton had to write the DOS on punch cards for compilation on a National Semiconductor IMP-16, which would spit the assembled code out onto a paper tape. Steve Wozniak, who was responsible for creating the disk controller for the machine, also made a plug-in card to read the paper tapes so that Laughton could debug the code.
Laughton describes more of the history here. ®