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Date:    19960502
From:    Steve Jones <>
Subject: Re: Recommended real-time OS for 386EX ?

Isaias Rafael B. Angeles, Jr. wrote:

Niilo Minkkinen wrote:
Please, recommend OS for embedded ( diskless ) solution using 386EX processor.
The OS should be royalty-free.
There is a free MSDOS compatible OS for the PC line, it is called FREEDOS and can be found in the INTERNET. This product was inspired by the LINUX project. They have a freeware C-COMPILER and the C source code for MSDOS so you can customize it for you application. It is not diskless but you can work your way around. The files are about 3MB in compressed form and consumes 10MB when extracted. Maybe you can use this as starting block and come up with another project for the embedded market. I myself would need a freeware program like that, so I would support this project if someone organizes this.

Right now, I do not have the necessary financial support to enable me to pursue this but I would like to do this in the near future.

I would be interested in the future development of this so I hope you can include me in your mailing list. I will also keep you my mailing list in case I find a source for this.


I noticed that there is some interest in a real-time, MS-DOS compatible operating system that can load .EXE's built with DOS tools. There are ten DOS codebases that I know of; some are commercial and some are freeware (and some are discontinued :).) Because I wrote a real-time DOS called Embedded DOS 6-XL after leaving Microsoft's NT group, I had an interest in collecting these and cataloging them.

XDOS I obtained from a guy who now works at Phoenix Technologies. It is small in size, written entirely in assembler, and not real-time in the sense that it does not provide a way to specify priorities for codepaths or guarantee delivery of service in a specified amount of time. It has no scheduler other than the normal "process scheduler" of MS-DOS. I got full source code and spoke with Thierry Giron, the author, and it's an all-around good piece of work.

RTDOS written by Mike Podanoffski is an interesting DOS that by its name and comments in the code would seem to offer threads, timers, and other stuff common to real-time kernels. It comes in book form and is available in computer bookstores. It does not actually have real-time elements, but does have MS-DOS compatible SFT, CDS, and other undocumented structures. The book is cheap and worth getting because it offers some good information for those writing a DOS. I wish I had that information before I began, although there is plenty more that needs to be accumulated before starting to write your own.

I once looked at the FREEDOS project but was confused about where the source to the kernel actually was, and it wasn't clear if there was a real-time scheduler available in the system. I would like to learn more about it if anyone has a pointer to the code on the net.

There are a bunch of DOSes out there making lots of money of course, such as DR-DOS (acquired by Novell but dumped after they discovered that it didn't have a compatible CDS or SFT). Novell DOS 7 is now discontinued, according to a news bulletin from Novell. That leaves MS-DOS which is officially dead according to Microsoft, and ROMDOS from datalite (used typically in mobile electronics according to their literature).

General Software has three DOSes for embedded uses. Since part of the original mail I'm responding to included an interest in getting the cost down on such an O/S, I'm providing some basic information here about pricing and source code availability, but for real detail, please see the web site or send email directly.

Embedded DOS 6-XL is a fully-reentrant DOS that runs from RAM. It has at its core a real-time scheduler with threads, timers, mutexes, events, message ports, queues, and so on. The DOS kernel uses these objects to make sure that when multithreaded apps use DOS calls simultaneously (i.e., call DOS from different threads at once), the critical sections of code and data are handled with kernel objects, not with disabled interrupts. Full source is available for the system files, device drivers, utilities, and ($2,500). Royalties are $15/copy and down depending on volume.

The second DOS is called Embedded DOS-ROM, and it runs directly from ROM, typically in less than 32KB. It has no scheduler. Its goals are to be small, fast, simple, and low-cost. Full source is available for $995. Royalties are $7.50/copy and down, depending on volume.

The third DOS is called Mini-DOS, and it is licensed free with our Embedded BIOS 3.1 product, in the same way that BASIC came with the IBM PC ROM BIOS. This DOS runs from ROM as a part of the BIOS and occupies 32KB->64KB, depending on how you configure it. Full source is standard with the BIOS kit ($4995).

If anyone knows of other DOS codebases, please let me know so I can get one for my collection. Thanks!

Steve Jones
Tel. (800) 850-5755 (toll free in US and Canada)
Tel. (425) 454-5755 (all other calls, overseas)
Fax. (425) 454-5744

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