The GEMDOS Story

Martin Döring — 02/18/2021

GEMDOS was first used in Apple's Lisa, and later, when home computers came along, in the Atari ST computers. In both, GEMDOS is the basis for GEM, the graphical user interface that became very popular with the introduction of the Atari STs.

The History

In 1999 Caldera bought both GEM and GEMDOS and toyed with the idea of developing a thin client on this basis. But this never really happened, and they then decided to release GEMDOS, along with GEM, under the GPL.

GEMDOS is a singletasking operating system, but is still able to manage multiple processes. This is also supported by GEM: one main program can be started, and up to 6 desktop accessories can run simultaneously.

GEMDOS, as it is available in the original source code, consists of two parts: The BIOS and the BDOS, which together is roughly what is known in the Atari community as TOS, if you leave out the graphics for a moment. The code presented here is just the 68000 implementation of GEMDOS. On the x86 platform, MSDOS has always been used as the basis of GEM.

To the GEMDOS Digital Research additionally provided some 68k development tools to compile and then bind the single modules. This is, compared to today's development environments, not very convenient. There was a 3-pass K&R C compiler from Alcyon, an assembler, a linker, and something in the way of utilities around it.

All this has been obsolete for a long time. GEMDOS has been replaced on the Atari by a far superior operating system called MiNT (MiNT is now TOS). This has been used for years on the Atari ST and TT still in use because it is more POSIX oriented and offers modern features such as memory protection, a multi-user environment and so on.

The provided BIOS source code could be interesting. It is generic and can be customized for specific hardware. There are very interesting routines in it that are needed in all implementations. Maybe you can do something with it, or you can just take a look at it and learn from it. There is no code from Atari in the Digital Research archives yet.

All the stuff provided here originally came from the so-called GEM world archives. But it seems that some copyright issues had been unclear.

The License

All sources I can provide here are now owned by Lineo and released under the GPL (General Public License) of the FSF (Free Software Foundation), version 2. At first the copyright was not really clear, because GEM was released under the GPL license, but nobody knew if the same was true for GEMDOS. Here is my former request from Dylan Harris to Lineo:

                      From: "Dylan Harris" <>
                       To: <>
04/19/01 01:18 AM cc:<>

Subject: GEMDOS and the GPL

    Hi, I've been informed that lineo now own GEMDOS,
original part of Digital Research's GEM package, which I had understood
to be the property of Caldera Inc.
    I ask this because Caldera, SFAIK, made GEM
and GEMDOS open source, so I raided all my old GEM archives and put all
my GEM bits and pieces up on my web site,
including my copy of the GEMDOS and GEM 68000 porting kit. There is also
some of my own code from that period. This was a few years ago now.
    Does lineo own GEMDOS? Is it released under
the GPL? If so, do you have any object with the content of my site? How
should I update the (c) notices. I don't want to tread on anyone's toes!

Dylan Harris
Cyberspace Services Ltd Dylan

And this is what Tim Bird, chief technology officer of Lineo, replied:

    You are informed correctly.  Lineo released
GEM under GPL a few years ago.  You have our permission to continue
collecting, using and distributing these old technologies. Caldera, Inc.
is the company that actually made the software available under the GPL. 
This company split into two and Caldera itself disappeared last year. 
Lineo (formerly under a different name) has continued selling DRDOS, and
now primarily sells Embedded Linux software.

    Caldera Systems is not related to this software,
and sells desktop and server Linux software. The GEM software may now be
used for any purpose (commercial or non-commercial) under the terms of
the GPL (the primary requirement of which is that the source code must
be made available for all derivative works).

    What is listed on your front page (GEM, GEMDOS,
GEM Programmer's Workbench, and GEM XM) all fall in this category. The
DRDOS software is still property of Lineo, and may be used for certain
non-commercial uses, as outlined in our former (7.02) license. Hopefully
this helps. If needed, this e-mail can serve as our release to you for
the purposes of using this software. Thanks,

Lineo, Inc.

Chief Technology Officer                 
390 South 400 West                          
Lindon, UT 84042

GEMDOS Download

Now here is all the old stuff I could find. There are three archives, here for download - as they are.


This is the last GEMDOS version from Digital Research that I know of. Later versions seem to have been further developed by Atari or other licensees themselves. These are not freely available. The most recent file in this archive is dated March 14, 1988. I don't know what the connection was with Atari's development team. All sources in this archive were so released under the GPL by Lineo. Included is also a GEMDOS documentation in mss format.


These are the original development tools to port GEMDOS to new platforms. They include a complete GEM consisting of VDI and AES, an assembler and an archiver (ar). Again, all sources in this archive are under the GPL. I know nothing about the licensing of the development tools. They come as they are.


This is the former development package from Digital Research for the Atari ST. It allows the developer to compile and link GEM programs - programs as well as desk accessories. Included is a C compiler, a linker and a resource construction set. All sources are under the GPL.

The Future

You think GEM has no future? Well, in September 2020 version 1.0 of EmuTOS has been released, about 20 years after I started to port GEM and BDOS to the Atari ST.

🌐 My first checkin to cvs

I'm long out of this project, but some brave guys had been constantly working on it. And, there it is in 2020:

🌐 EmuTOS 1.0 Youtube Presentation
🌐 The EmuTOS Website

Data Privacy Statement