The development of Atari Basic and Atari DOS
I don't know exactly when the concept of the Atari Computer
was developed within the corporate mind of Atari, Inc., nor do I know all
of the people responsible for nursing that concept into reality. The following
history covers the relationship with Atari, Inc., during the evolution
of the system software.
Sometime in early 1978, when the Atari 800 and 400 were
still called "Coleen" and "Candy" and were still in
the breadboard stages, Atari bought a copy of the source for Microsoft
8K BASIC. This version of BASIC was fundamentally the same product that
was implemented by Commodore in the early PETs, was used by OSI, and was
a close ancestor of Microsoft's Applesoft Basic. Six months and many, many
Atari man-hours later, that 8K BASIC was almost functioning properly on
the Atari prototypes. But buying source for a program buys you just that:
source. Generally, you also receive little documentation, sometimes obscure
code, no guide to modification, and no real support. What to do? The products
were due to be shown in early January, 1979, at the Consumer Electronics
Show (CES) in Las Vegas, Nevada.
Enter Shepardson Microsystems, Inc (SMI), my employer
at that time. Though little known by the microcomputer public, SMI had
already produced some very successful, private labeled microcomputer software.
Among our better-known efforts were the original Apple DOS, Cromemco 16K
Extended BASIC, and Cromemco 32K Structured BASIC (just being completed
at that time). Also, we had done some work for Atari on a custom game processor.
(Which used a 12-bit ROM and 5-bit RAM configuration and was well received
at Atari, but never produced.)
Coincidentally, about that same time SMI had also purchased
source for Microsoft 6502 BASIC. After producing Apple's DOS, we had the
bright idea of mating the Apple II peripheral bus with the KIM/SYM/AIM
system bus (and it still seems like a good idea to us, but...). The idea
was to provide a disk system (Apple's) to the Single Board Computer market.
Needing a BASIC to sell with the system, we plunked down a few grand and
purchased Microsoft's. Though it looked to us like it would be difficult
to modify, we were intending to resell it with a minimum of changes, so
it seemed appropriate.
A New BASIC?
Re-enter Atari, some time in the late summer of 1978,
asking if SMI could help them. With Microsoft BASIC? Well ... we really
didn't want to, but... Could we propose a new BASIC? We talked. And had
meetings, and a study contract, and more meetings, and finally we wrote
a specification for a 10K, ROM-based BASIC. (I still have a copy of that
spec, and it's amazing how little the final version deviated from that
Of course, in the middle of all these discussions, Atari
naturally divulged how their (truly superb) ROM-based Operating System
would interface both with BASIC and with various devices. Somewhere in
here, my memory of the sequence of events and discussions becomes a little
unclear, but suffice it to say that we found ourselves making a bid on
producing not only a BASIC for Atari, but also the file Manager (disk device
driver) which would change Atari OS to Atari DOS.
Sometime in late September, 1978, the final proposal was
made to Atari, and it was accepted by them shortly thereafter. In mid-October,
1978, we received the go-ahead. The project leader was Paul Laughton, author
of Apple DOS. The bulk of the work ended up being done by Paul and Kathleen
O'Brien. Though I was still involved in the finishing touches on Cromemco
BASIC, I take credit for designing the floating point scheme used in Atari
BASIC. Paul Krasno implemented the math library routines following guidelines
supplied to us by Fred Ruckdeschel (author of the acclaimed text, BASIC
Scientific Subroutines). And, of course, much credit must go to Mike Peters,
our combination keypuncher/computer operator/junior programmer/troubleshooter.
Since we obviously couldn't have the Atari machines to
work on (they hadn't been built yet), the first step was to bring up an
emulator for Atari's CIO ("Central Input-Output," the true heart
of Atari 's OS) on our Apple II systems. With Paul Laughton leading the
way (and doing a lion's share of the work), the pieces fell together quickly,
"Little" things had to be overcome: the cross-assembler was modified
to handle the syntax table pseudo-ops, the 256-byte Apple disk sectors
had to be made to look like 128-byte Atari sectors, the BASIC interpreter
seemed to function, but was waiting for the floating point routines. And
there are funny things to tell of, also. Like our cross-assembler, running
on an IMP-16P (a 1973 vintage, 16-bit, bit-sliced PMOS microprocessor)
that used keypunched cards for input, a floppy disk (with no DOS) as temporary
storage, and a paper tape punch as output.
Somehow, Kathleen and Paul guided the two programs unerringly
toward completion. On December 28, 1978, Atari's purchasing department
at last delivered a signed copy of the final purchase order. It called
for delivery of both products by April 6, 1979. There was a clause which
provided for a $1,000 per week incentive (if we finished early) and penalty
(if we finished late). What is especially humorous about that December
28th date is that the first working versions of both BASIC and FMS had
already been delivered to Atari over a week before! That is fast work.
Fortunately, then, Atari took their new Atari BASIC to
CES. Unfortunately, there was a limit on the amount of incentive money
collectible. Oh, well.
In the months that followed, SMI fixed bugs, proofread
manuals, and worked on other projects (including the Atari Assembler/Editor,
which was mostly Kathleen's effort). The nastiest bugs in BASIC were fixed
by December, 1979, but it was too late: Atari had already ordered tens
of thousands of BASIC ROMs. The FMS bugs were easier to get fixed, since
DOS is distributed on disk.
In mid-1980, Paul Laughton once again tore into FMS. This
time, he modified it to handle the ill-fated 815 double-density disk drive
and added "burst I/O" (and there will be much more about both
these subjects in the technical discussion that follows).
In late 1980, and early 1981, Bob Shepardson, owner of
Shepardson Microsystems, Inc., decided that the pain and trouble of having
employees wasn't justified by the amount of extra income (if any) that
he derived. Though we still occasionally function in a loose, cooperative
arrangement, the halcyon days of SMI seem to be over.
I negotiated with Bob Shepardson for his rights to the
Atari products (FMS, BASIC, and the Assembler/Editor) and their Apple II
counterparts. Thankfully, Atari had purchased from SMI only a non-exclusive
right to distribute these products. SMI had retained the rights to license
other users on a similar non-exclusive basis (and, indeed, SMI sold a version
for the Apple II during most of 1980).
So now it was frantic time again: this was February 25, 1981, and the West Coast Computer Faire was April 3rd. But our brand new company, Optimized Systems Software, arrived on time, bringing with it BASIC A +, OS/A + and EASMD. All three were enhanced, disk-based versions of the original Atari programs (and, in fact, derived some of their enhancements from the previous 055 Apple II products).
The products have been well received by the Atari user
community, in part due to the fact that they are truly compatible, yet
enhanced, versions of standard Atari software.
Why This Book?
The decision to publish these listings was not an easy
one to make; and it is, in its own way, an historic occasion. After all,
have you ever seen anyone offering source or listings of CP/M, the most
popular of all computer operating systems? Since Atari, to their credit,
has honored the original agreement with SMI and not released either source
or listings without permission, the responsibility for doing so seemed
to rest with OSS.
But Atari has set a powerful precedent by publishing the
listings of DUP (their portion of DOS 2.OS) and the OS ROMs. The clamor
from Atari users for the source for FMS finally even reached us, so we
have bowed to the inevitable, and honored the same commitment that Atari
has made: to release as much information and aid as possible to the user
We hope that the users will appreciate these efforts and,
in turn, respect our rights and Copyrights. As long as there is a mutual
respect and benefit, you, the user, can expect continued support.
About This Book
With the release of this book, the dedicated Atari enthusiast
can examine all the the inner workings of Atari DOS and modify his (or
her) system to his heart's delight Rather than simply publish listings,
we have chosen also to provide a complete guide to the workings of FMS.
Although the listing itself is relatively clear and commented,
all but the most expert would have trouble plowing through some of the
tortuous logic necessary in such a program. The guide included here describes
all aspects of the FMS, including the external view, the charts and tables,
the various interfaces, and (in copious detail) the functions of the individual
subroutines (including complete entry and exit parameters).
There is much of value here even for the person who never
intends to modify Atari DOS. We feel that FMS is a fairly well-structured,
relatively sophisticated, system level assembly language program. We hope
that most users will gain by the insights presented here.
We would welcome any notes you would care to send pointing
out errors either in the DOS or in this book.
Optimized Systems Software
If you would like to contact Bill, you can Email him at: firstname.lastname@example.org