I've always had a fascination with Atari DOS 1, released in 1979 with the
Atari 810 disk drive for the Atari 800 computer.  It was replaced quickly
with DOS 2 that fixed a number of bugs, and improved performance.  DOS 1
used a lot more memory because it included the user utilities permanently
loaded in memory, which was inefficient, but very convenient when
programming in BASIC.  DOS 1 also only used a single boot sector, while DOS
2 used three.

The assembly source listings for DOS 2 were published in "Inside Atari DOS"
by Bill Wilkinson, published by COMPUTE! Books.  I still have my copy.
This has the listings only for DOS.SYS (including the boot sectors).  The
source for DOS 1 was never published.  At some point the listings for the
DUP portion of DOS 1 were leaked, and the PDF that I found is included
here.  It's a grainy scan of a printout that often cuts off the last line
or two from each page.

To have good, working source files, I took a copy of DOS 1 and disassembled
it.  The boot sector is at $700, immediately followed by DOS.SYS at $780.
I split it into two files for the sources:
  dos1dos.asm
  dos1dup.asm

The dos1dos.asm is the output from my disassembler after manually setting
many labels based on the DOS 2 sources.  Many more could be corrected this
way, and many comments could be added back in to get something very close
to the original listings, but what I have now is a pretty good start.

The dos1dup.asm is as close to a perfect match for the printout from 1979.
I started with my disassembly and went through and adjusted it to match the
listings exactly, with a few notes added by me in square brackets.  I've
assembled these sources and verified that it matches my binary with the
exception of data fields that change.

One addtional file is:
  dos1dos.labels
This is an input file for my disassembler that sets label names and types.
I've added a bunch of comments in this file.

I would like to eventually get dos1dos.asm cleaned up with all the correct
labels and comments from DOS 2 or rewritten to match as best as we can
guess.  Unless, of course, someone comes up with original listings.

I also intend to include modified sources to fix bugs and save memory.
Contributions are welcome!