DeveloperDigital Research
Written inC
Working stateDiscontinued
Source modelClosed source
Initial release1986; 38 years ago (1986)
Latest release2.33 / May 1998; 25 years ago (1998-05)
Latest preview2.34 / 1999; 25 years ago (1999)
Marketing targetIndustrial, PoS
Available inEnglish
PlatformsIntel 80186, Intel 80286, Intel 80386, Motorola 68000, V60, V70
Kernel typemodular
user interface
various frontends, X/GEM
Preceded byConcurrent DOS 286, Concurrent DOS 68K, Concurrent DOS V60[1]
Succeeded byS5-DOS/MT, 4680 OS, 4690 OS

FlexOS is a discontinued modular real-time multiuser multitasking operating system (RTOS) designed for computer-integrated manufacturing, laboratory, retail and financial markets. Developed by Digital Research's Flexible Automation Business Unit in Monterey, California, in 1985,[2][3] the system was considered to become a successor of Digital Research's earlier Concurrent DOS, but with a new, modular, and considerably different system architecture and portability across several processor families.[4] Still named Concurrent DOS 68K and Concurrent DOS 286, it was renamed into FlexOS on 1 October 1986 to better differentiate the target audiences. FlexOS was licensed by several OEMs who selected it as the basis for their own operating systems like 4680 OS, 4690 OS, S5-DOS/MT and others. Unrelated to FlexOS, the original Concurrent DOS system architecture found a continuation in successors like Concurrent DOS XM and Concurrent DOS 386 as well.


Concurrent DOS 286, Concurrent DOS 68K and FlexOS were designed by Francis "Frank" R. Holsworth (using siglum FRH).[5][6] Like Portable CP/M, Concurrent DOS 286, Concurrent DOS 68K and Concurrent DOS V60,[1][7] FlexOS was written in C for higher portability across hardware platforms, and it featured very low interrupt latency and fast context switching.[8]

The original protected mode FlexOS 286 version 1.3[9] was designed for host machines equipped with 286 CPUs, and with adaptations for NEC V60, NEC V70 and Motorola 68000 processors planned.[4][1][7] FlexOS 286 executables using the system's native INT DCh (INT 220) application program interface had the filename extension .286. A CP/M API front-end (FE) was available as well,[10] using the extension .CMD for executables. (A filename extension of .68K was reserved for FlexOS 68K, a file extension derived from Concurrent DOS 68K as of 1986.[11][7][12][10])

In May 1987, FlexOS version 1.31 was released for 80286 machines.[13] The developer version required an IBM PC/AT-compatible machine with 640 KB of conventional and 512 KB of extended memory, and either a (monochrome) CGA or an EGA graphics adapter.

FlexOS supported a concept of dynamically loadable and unloadable subdrivers, and it came with driver prototypes for floppies, hard disks, printers, serial interfaces, RAM disks, mice and console drivers.

During boot, the FLEX286.SYS kernel would load the resource managers and device drivers specified in the CONFIG.SYS binary file (not to be mixed up with the similarly named CONFIG.SYS configuration file under DOS), and its shell (COMMAND.286) would execute a CONFIG.BAT startup batch job instead of the common AUTOEXEC.BAT.

FlexOS's optional DOS emulator provided limited PC DOS 2.1 compatibility for DOS .COM and .EXE programs.[9] Certain restrictions applied in "8086 emulation mode" since these programs were executed in the processor's protected mode. Due to bugs in earlier steppings of the Intel 80286, the FlexOS 286 DOS front-end required at least the 80286 E2 stepping to function properly (see LOADALL).[9] These problems had already caused delays in the delivery of Concurrent DOS 286 earlier.[14][15]

The system optionally supported a multitasking GEM VDI for graphical applications.[9][16]

FlexOS 1.31 could be linked with none, either or both of these two modules. FlexOS 1.31 also supported FlexNet.

By June 1987 there were also versions 1.0 of FlexOS 386 (for hosts) and FlexOS 186 (for remote cell controllers).[8] FlexOS 386 provided a windowing feature, and offered PC DOS 3.2 and GEM compatibility.[8]

FlexOS 286 and FlexOS 386 versions 2.0 were registered on 3 July 1989.

Among the major FlexOS customers in 1990/1991 were FANUC, IBM, ICL, Nixdorf, Siemens, TEC, Thorn EMI Software and Micrologic.[3][17]

Novell bought Digital Research for US$80 million[18] in July 1991.[19][3][20][18]

X/GEM for FlexOS release 1.0 (a.k.a. X/GEM FlexOS 286 and 386) and FlexNet were registered on 21 December 1992.

FlexOS was used as the primary test platform for the new Novell Embedded Systems Technology (NEST).[21]

When Novell decided to abandon further development of the various Digital Research operating systems such as Multiuser DOS (a successor to Concurrent DOS) and Novell DOS (a successor to DR DOS), they sold FlexOS off to the Santa Clara, California-based Integrated Systems Inc. (ISI) for US$3 million in July 1994.[22] The deal comprised a direct payment of half this sum as well as shares representing 2% of the company. The company already had pSOS+, another modular real-time multitasking operating system for embedded systems, but they continued to maintain FlexOS as well.[22] FlexOS version 2.33 was current as of May 1998 and with FlexOS 2.34 to be released soon after with added support for faster CPUs, 64 MB of memory, EIDE and ATAPI CDROM drives.

Integrated Systems was bought by their competitor Wind River Systems in February 2000.


The following list of commands is supported by FlexOS:[23]


Known FlexOS versions include:

Motorola 68000 / Freescale/NXP ColdFire MCF5251[24] platform:

Intel 80286 platform:

Intel 80186/NEC V20/V30 platform:

Intel 80386 platform:

NEC V60 platform:


IBM 4680 OS

Named IBM 4680 OS Version 1, IBM originally chose DR Concurrent DOS 286 as the basis of their IBM 4680 computer for IBM Plant System products and Point-of-Sale terminals in 1986.[32][10][4][33] The last release of the IBM 4680 OS has been Version 4, before it was replaced by IBM 4690 Version 1.[34]


IBM and Toshiba 4690 OS

Main article: 4690 Operating System

In July 1993, IBM announced the adoption of FlexOS version 2.32 as the basis of their IBM 4690 OS Version 1, to be pre-released on 24 September 1993[33] and generally made available from 25 March 1994.[34][35] FlexOS 2.32 supported 286 and 386 modes, had more efficient memory management, better console and pipe systems, and brought overall quality and performance improvements compared to the version that came with IBM 4680 OS Version 4.[34] Further, it removed limits on the number of applications running concurrently due to its more efficient use of KOSPOOL.[34]

To support Java, IBM 4690 OS Version 2 added support for long filenames by means of a virtual filesystem (VFS) architecture and it introduced FAT32 volumes.

According to "The Year of the Store?", IHL Consulting Group/RIS News, IBM 4690 OS still had a market share of 12% in the POS register/client market in June 2005, when IBM was starting to phase it out in favour to IBM Retail Environment for SUSE (IRES).[33]

IBM continued to maintain 4690 OS up to April 2015, with the most recent version released by IBM in May 2012 being IBM 4690 OS Version 6 Release 3.

Toshiba released Toshiba 4690 OS Version 6 Release 4 in January 2014 and Version 6 Release 5 in January 2016.

Siemens S5-DOS/MT

Siemens used and still maintains FlexOS in their factory automation equipment as well. For example, their Simatic S5 STEP-5 operating system S5-DOS/MT is based on FlexOS 386 with X/GEM, FlexNet and Btrieve, whereas the smaller S5-DOS system, also present on these systems, is a variant of Digital Research's Personal CP/M-86.

Siemens industrial systems like COROS LS-B/FlexOS, COROS OS-B/FlexOS, GRACIS/FlexOS, Teleperm M [de] OS-525 were FlexOS and X/GEM-based.

Computers such as the Sicomp [de] PC 16-20 and the PC 32 series were available with FlexOS as well.


The Japanese post office shared terminals CTM [ja] III and CTM IV were based on FlexOS.

See also


  1. ^ a b c d Glass, Brett (1991-05-06). "Answer Line". InfoWorld: 72. ISSN 0199-6649.
  2. ^ Watt, Peggy (1986-10-27). "Digital Research tighens belt with layoffs, reorganization - Realign business units, product lines". Computerworld - The Newsweekly for the Computer Community. Computer Industry. Vol. XX, no. 43. Monterey, California, USA: CW Communications, Inc. p. 95. ISSN 0010-4841. Archived from the original on 2020-02-16. Retrieved 2020-02-16.
  3. ^ a b c "Novell and Digital Research sign definitive merger agreement". Business Wire. 1991-07-17. Archived from the original on 2018-08-18. Retrieved 2017-01-24.
  4. ^ a b c CBR, ed. (1987-01-15). "Digital Research launches FlexOS 286 Real-Time Manufacturing Operating System". Computer Business Review. Archived from the original on 2013-01-18. Retrieved 2018-09-15.
  5. ^ Wein, Josef "Joe" (2002). "Gary Kildall in England". Archived from the original on 2019-04-03. Retrieved 2019-04-03.
  6. ^ Holsworth, Francis "Frank" R. (2006-02-01). "Video: Frank Holsworth, developer" (interview). Information Technology Corporate Histories Collection. Computer History Museum. CHM Catalog Number 102770341. ITCHP 44403c1a3fd53. Lot Number X7847.2017. Archived from the original on 2019-04-03. Retrieved 2019-04-04.
  7. ^ a b c d e f g h i j "Concurrent DOS 68K 1.2 - Developer Kit for Motorola VME/10 - Disk 2". 1986-08-06 [1986-04-08]. Retrieved 2018-09-13. (NB. Also contains header files from Concurrent DOS 286, and some hints on the existence of a Concurrent DOS V60. STRUCT.H mentions LOADALL for "8086 emulation".)
  8. ^ a b c CBR, ed. (1987-06-03). "Digital Research shows off Real-Time FlexOS 386". Computer Business Review. Archived from the original on 2013-06-28. Retrieved 2011-09-06.
  9. ^ a b c d e FlexOS Supplement for Intel iAPX 286-based Computers (PDF). 1.3 (1 ed.). Digital Research, Inc. November 1986. Archived (PDF) from the original on 2021-09-03. Retrieved 2018-08-14.
  10. ^ a b c "IBM selects Concurrent DOS-286 for PC AT retail system" (PDF). European Review. Digital Research (18): 1. March 1986. Retrieved 2018-09-15.
  11. ^ a b c "Concurrent DOS 68K 1.2 - Developer Kit for Motorola VME/10 - Disk 1". 1986-08-06 [1986-04-08]. Retrieved 2018-09-13.
  12. ^ a b c "Concurrent DOS 68K 1.2 - Developer Kit for Motorola VME/10 - Disk 3". 1986-08-06 [1986-04-08]. Retrieved 2018-09-13.
  13. ^ a b FlexOS 286 Version 1.31 - Release Note 01 (PDF). 1.31 (1 ed.). Digital Research, Inc. May 1987. 1073-1001-002. Retrieved 2018-09-14.
  14. ^ a b Foster, Edward (1985-05-13). "Super DOS awaits new 80286 – Concurrent DOS 286 – delayed until Intel upgrades chip – offers Xenix's power and IBM PC compatibility". InfoWorld. InfoWorld Media Group. 7 (19): 17–18. ISSN 0199-6649.
  15. ^ Foster, Edward (1985-08-26). "Intel shows new 80286 chip – Future of DRI's Concurrent DOS 286 still unclear after processor fixed". InfoWorld. InfoWorld Media Group. 7 (34): 21. ISSN 0199-6649.
  16. ^ CBR, ed. (1988-04-05). "Digital Research, profitable for fiscal 1987, comes out of the closet". Computer Business Review.
  17. ^ Digital Research (1990-06-04). "Sold on FlexOS". Computerworld (Advertisement). XXIV (23). Retrieved 2017-01-24.
  18. ^ a b Schulman, Andrew; Brown, Ralf D.; Maxey, David; Michels, Raymond J.; Kyle, Jim (1994) [November 1993]. Undocumented DOS: A programmer's guide to reserved MS-DOS functions and data structures - expanded to include MS-DOS 6, Novell DOS and Windows 3.1 (2 ed.). Addison Wesley. p. 182. ISBN 0-201-63287-X. (xviii+856+vi pages, 3.5-inch floppy) Errata: [1][2]
  19. ^ Scott, Karyl (1991-07-29). "Novell/DRI merger to reap better client management". InfoWorld. Networking. Vol. 13, no. 30. InfoWorld Publishing Co. p. 33. ISSN 0199-6649. Archived from the original on 2020-02-09. Retrieved 2017-01-21.
  20. ^ Allchin, Jim (1992-05-27) [1991-07-17]. "Novell/Digital Research reach definitive agreement…" (PDF) (Court document). Plaintiff's exhibit 828, Comes v. Microsoft. Archived (PDF) from the original on 2016-11-19. Retrieved 2017-01-21.
  21. ^ "Novell Announces RTOS Vendor Program Which Brings Integrated Networking Solutions to the Embedded Systems Marketplace" (Press Release). Novell. 1995-05-23. Because Novell used Integrated Systems' FlexOS during the development and testing of NEST, we are in the unique position of supporting it through both our real-time product lines pSOSystem for deeply embedded markets, and FlexOS for point of sale," said Moses Joseph, vice president of marketing for Integrated Systems. "Developers using the FlexOS development kit and the expanded pSOSystem/NEST package for everything from home security and entertainment to office automation and global communications applications, now have quick and easy access to the widest variety of standard networking protocols.
  22. ^ a b "pSOSystem and the NEST Development Environment - Designing Embedded Applications with NetWare Connectivity" (White paper). Integrated Systems, Inc. (ISI). 1998. Archived from the original on 1998-02-19.
  23. ^ FlexOS User's Guide Version 1.3 (PDF). 1.3 (1 ed.). Digital Research. November 1986. 1073-2003-001. Archived (PDF) from the original on 2019-03-30. Retrieved 2019-04-23.
  24. ^ a b "MCF5251 Product Brief - ColdFire 32-Bit Processor" (PDF) (Product flyer) (Revision 0 ed.). Freescale Semiconductor, Inc. June 2006. MCF5251PB. Archived (PDF) from the original on 2018-09-15. Retrieved 2018-09-15.
  25. ^ Gallant, John (1984-01-23). "Digital Research, Monterey ink Unix-centered pact". Computerworld. XVIII (3): 6. Retrieved 2019-02-03.
  26. ^ Knox, James M. (1986-06-22). "Re: DRI Concurrent DOS for 68K". Newsgroupmod.computers.68k. Archived from the original on 2018-09-13. Retrieved 2018-09-13.
  27. ^ a b Heller, Robert; Taetsch, Tom (1987-01-29) [1987-01-26, 1987-01-27]. "Concurrent DOS 68K: The word from DRI". Newsgroupmod.computers.68k. Archived from the original on 2020-01-03. Retrieved 2010-01-03. […] it is possible to purchase an implementation of CDOS-68K for the Motorola VME-10. The media it comes on is Motorola VME-10 5.25" floppies. […] CDOS-68K is the 68K version of CDOS-286 (which has now been updated and renamed to FlexOS 286). This CDOS-286/68K operating system was designed specifically to provide easy addition and deletion of I/O drivers and sub-drivers. Drivers can either be linked in to the O/S or kept external and dynamically loaded at boot time. […] CDOS-68K is at revision level 1.2, while CDOS-286 was upgraded to rev level 1.3 (at which point it became FlexOS 286). The significance of this to you is that no enhancements or maintenance of the 68K version is planned in the near future (unless a "major" OEM contract should happen). So the 68K O/S is pretty much being sold only on an "as is" basis. […]
  28. ^ Swaine, Michael (1982-04-05). "Homebrew Computer Club views Intel's superchip". InfoWorld. Palo Alto, CA, USA. 4 (13): 4. Archived from the original on 2020-01-07. Retrieved 2020-01-07. […] Digital Research is producing an operating system for the 286. MP/M-286 will take advantage of the processor's memory management and protection and virtual memory support. Digital Research is promising "complete" compatibility with its MP/M-86 and CP/M-86 for the 8086 processor. Intel is supplying Digital Research with the hardware to develop and test MP/M-286. […]
  29. ^ Bidmead, Christopher H. (2006-05-09) [1985-03-25]. "Surviving Big Blue". Doctor Who. Which Computer?. Archived from the original on 2020-01-07. Retrieved 2020-01-07. […] Paul Bailey of Digital Research keenly promotes this approach; it is his company that is supplying ICL and others with Concurrent Dos-286. This chameleon operating system allows ICL and other 80286 manufacturers to build machines that will be able to cope with all the existing body of IBM-PC software -- and at the same time promise multi-tasking, windowing and true concurrency, three features that together allow a single micro to do several things at once. […] Although no firm announcements have been made, it seems certain that by the end of the year ACT will be offering a Concurrent CP/M 286 machine to fuel its drive into the corporate market. But by this time it will have to contend with IBM's own 80286 office micro, the PC/AT. […] IBM also have a software product in the offing that could pull the rug out from under the Concurrent contenders. Some 180K in size, TopView is a program for IBM PC's and AT's that beefs up the operating system to provide windowing facilities for existing 'well behaved' standard packages. […]
  30. ^ "Concurrent DOS-286 Challenges Unix". BYTE Magazine. 10 (5): 375-377. May 1985. Archived from the original on 2018-09-14. Retrieved 2017-01-23. [3]
  31. ^ High C Programmer's Guide - Version 1.2 for Concurrent DOS (PDF) (1 ed.). Santa Cruz, CA, USA: MetaWare Incorporated. 1986 [1985-09-15]. Retrieved 2018-08-14. This is a guide to the operation of the High C compiler as implemented for the Concurrent DOS 286 1.2 or later operating system - hereafter abbreviated to just "Concurrent" per Digital Research custom - running on the Intel 80286 microprocessor and using the Intel Object-Module Format (OMF). The compiler generates code for any of the Intel 8086/88/186/188/286 family of microprocessors.
  32. ^ Calvo, Melissa; Forbes, Jim (1986-02-10). "IBM to use a DRI operating system". InfoWorld . Retrieved 2011-09-06.
  33. ^ a b c "How to choose the best OS for your point-of-sale" (PDF). Novell. 2005. Archived from the original (PDF) on 2006-01-17. Retrieved 2012-01-10 – via 360Commerce. (NB. This PDF has a short history of POS operating systems, also mentioning IBM 4680 and IBM 4690.)
  34. ^ a b c d IBM, ed. (June 1993). "IBM 4690 OPERATING SYSTEM VERSION 1 - Announcement Letter Number 293-281 dated 1 June 1993 - Brief description of announcement, charges, and availability". Retrieved 2011-09-06.
  35. ^ IBM (ed.). "IBM 4690 Operating System". Archived from the original on 2011-09-30. Retrieved 2011-09-06.

Further reading