FlexOS 286

FlexOS
Company type	Operating system
Industry	Computer software
Predecessor	Concurrent DOS
Founded	1985
Headquarters	Monterey, California, United States
Products	FlexOS operating system
Owner	Integrated Systems Inc. (since 1994)
Parent	Digital Research (until 1994), Novell (1991–1994)

FlexOS was a modular, real-time multitasking and multiuser operating system (RTOS) developed by Digital Research's Flexible Automation Business Unit in Monterey, California, launched in 1985. It was aimed primarily at sectors such as industrial automation, laboratory environments, retail operations, and financial services.

Initially designed to succeed Digital Research's Concurrent DOS, FlexOS introduced a modular design and was engineered for portability across various processor architectures. It began under the names Concurrent DOS 68K and Concurrent DOS 286, before being renamed FlexOS on October 1, 1986, to better define its market focus.

Multiple original equipment manufacturers (OEMs) adopted FlexOS as the core for their proprietary operating systems, including 4680 OS, 4690 OS, and S5-DOS/MT. Meanwhile, the Concurrent DOS lineage continued independently with subsequent versions like Concurrent DOS XM and Concurrent DOS 386.

Overview

The development of Concurrent DOS 286, Concurrent DOS 68K, and FlexOS was led by Francis "Frank" R. Holsworth (initialed FRH). Similar to Portable CP/M, these operating systems were written in the C programming language to ensure hardware platform independence, featuring rapid context switching and low interrupt latency.

The first protected mode iteration, FlexOS 286 version 1.3, targeted Intel 286 processors and was planned for adaptation to NEC V60, NEC V70, and Motorola 68000 CPUs. Executables for FlexOS 286 utilized a native INT DCh (INT 220) API with a .286 file extension; additionally, a CP/M-compatible API front-end supported .CMD files. The .68K extension was designated for FlexOS 68K binaries derived from Concurrent DOS 68K.

In May 1987, version 1.31 of FlexOS was released for machines with Intel 80286 processors. The development environment required an IBM PC/AT-compatible system equipped with 640 KB conventional memory and an additional 512 KB of extended memory, along with CGA or EGA graphics adapters.

FlexOS featured dynamically loadable subdrivers that included experimental support for floppy drives, hard disk drives, printers, serial ports, RAM disks, mice, and console devices. During system startup, the FLEX286.SYS kernel loaded resource managers and device drivers from a binary CONFIG.SYS file—distinct from the DOS CONFIG.SYS—while its shell component (COMMAND.286) executed a CONFIG.BAT batch script instead of the traditional AUTOEXEC.BAT.

An optional DOS emulator offered limited compatibility with PC DOS 2.1 programs (.COM and .EXE) running under protected mode but imposed certain restrictions. Due to early errata in Intel's 80286 processors, this DOS compatibility layer required at least the E2 stepping revision to operate correctly—an issue that had previously delayed Concurrent DOS 286’s release.

FlexOS also optionally supported multitasking graphical applications through integration with the Graphics Environment Manager (GEM) Virtual Device Interface (VDI). Version 1.31 allowed linking with zero, one, or both of these components and included support for Novell’s FlexNet networking system.

By mid-1987, FlexOS versions targeting different hardware were available: version 1.0 of FlexOS 386 for host computers and FlexOS 186 tailored for remote controllers. The FlexOS 386 variant introduced windowing capabilities and compatibility with PC DOS 3.2 as well as GEM.

On July 3, 1989, versions 2.0 of both FlexOS 286 and FlexOS 386 were officially registered for copyright protection.

Key clients during the period from 1990 to 1991 comprised companies such as FANUC, IBM, ICL, Nixdorf, Siemens, Toshiba TEC, Thorn EMI Software, and Micrologic.

Novell acquired Digital Research in July 1991 for $80 million. Subsequently, X/GEM for FlexOS release 1.0 along with FlexNet were registered on December 21, 1992.

FlexOS became the primary testing platform for Novell Embedded Systems Technology (NEST).

After Novell halted further development of Digital Research operating systems including Multiuser DOS and Novell DOS products, it sold FlexOS to Integrated Systems Inc. (ISI), based in Santa Clara, in July 1994 for $3 million—half paid upfront plus shares representing a two percent stake. ISI already owned pSOS+, another modular real-time OS aimed at embedded systems but continued supporting FlexOS post-acquisition.

As of May 1998, FlexOS version 2.33 remained current; plans existed for version 2.34 to add support for faster processors, up to 64 MB of RAM, EIDE storage devices, and ATAPI CD-ROM drives. A significantly upgraded version numbered 2.4 was also anticipated though its release status is uncertain.

In February 2000 Integrated Systems was purchased by competitor Wind River Systems, effectively ending active development of both pSOS+ and FlexOS platforms.

Commands

FlexOS incorporates a variety of commands that are vital for managing and operating the system:

ASSIGN
BACK
BACKUP
BREAK
CANCEL
CHDIR
CHKDSK
COMMAND
COMP
CONFIG
COPY
CTTY
DATE
DEFINE
DIR
DISKCOMP
DISKCOPY
DISKSET
ERASE
EXIT
FDISK
FIND
FORMAT
FSET
LIST
LOGOFF
LOGON
MKDIR
MORE
ORDER
PASSWORD
PATH
PRINT
PROCESS
PROMPT
RECDIR
RECFILE
RENAME
RESTORE
RMDIR
SECURITY
SORT
SYS
TIME
TREE
TYPE
VER
VOL

Versions

FlexOS was engineered for multiple microprocessor architectures, with several notable releases highlighting its development over time:

Motorola 68000 / Freescale / NXP ColdFire MCF5251 series:

- Concurrent DOS 68K versions 1.0 through 1.21 launched between 1985 and 1986 - FlexOS 68K iterations within the 1.x range

Intel 80286 architecture:

- MP/M-286 introduced in 1982 - Concurrent CP/M-286 released in 1985 - Concurrent DOS 286 line progressing from early 1985 previews to version 1.2 by 1986 - FlexOS 286 editions spanning from version 1.3 in November 1986 up to version 2.32 in July 1993

Intel 80186 / NEC V20 / V30 processors:

- FlexOS 186 branch originated in September 1986 - Version 1.0 of FlexOS 186 issued in June 1987

Intel 80386 CPU:

- Launch of FlexOS 386 occurred in June 1987 - Follow-up versions include release 2.0 in July 1989 extending to planned version 2.34 by 1999

NEC V60 hardware:

- Concurrent DOS V60, though less extensively documented, is referenced in early materials

These editions demonstrate FlexOS's progression alongside advancing CPU designs, catering to a wide array of embedded and real-time system applications.

IBM 4680 OS

In 1986, IBM chose DR Concurrent DOS 286 as the core for their IBM 4680 operating system, which powered IBM Plant System devices and Point-of-Sale terminals. The product line culminated with Version 4 before transitioning to IBM's subsequent release, IBM 4690 Version 1.

The versions released were:

IBM 4680 Operating System Version 1 Release 1
IBM 4680 Operating System Version 1 Release 2
IBM 4680 Operating System Version 1 Release 3
IBM 4680 Operating System Version 2 Release 1
IBM 4680 Operating System Version 3 Release 1
IBM 4680 Operating System Version 4 Release 1

IBM and Toshiba 4690 OS

In July 1993, IBM selected FlexOS version 2.32 as the foundation for IBM 4690 OS Version 1, which was initially previewed in September and became widely available by March 1994. FlexOS 2.32 offered enhanced support for both 286 and 386 processor modes, introduced advancements in memory management, improved console and pipe mechanisms, and delivered better overall performance compared to IBM 4680 OS Version 4. Additionally, it eliminated restrictions on simultaneous applications by optimizing KOSPOOL utilization.

The release of IBM 4690 OS Version 2 brought features such as Java integration, support for long filenames through a virtual filesystem (VFS), and the introduction of FAT32 volume compatibility.

By mid-2005, IBM 4690 OS still held approximately 12% of the POS register/client market share, despite IBM gradually transitioning toward IBM Retail Environment for SUSE (IRES).

IBM provided platform support until April 2015, with the final IBM-issued version being Version 6 Release 3 in May 2012. Development efforts were continued by Toshiba, which issued Versions 6 Release 4 in January 2014 and Release 5 in January 2016.

Siemens S5-DOS/MT

FlexOS remains in use within Siemens' factory automation solutions. The Simatic S5 STEP-5 operating system, known as S5-DOS/MT, is built upon FlexOS 386 and incorporates components such as X/GEM, FlexNet, and Btrieve. A more compact variant, S5-DOS, derives from Digital Research's Personal CP/M-86.

Siemens’ industrial operating systems—including COROS LS-B/FlexOS, COROS OS-B/FlexOS, GRACIS/FlexOS, and Teleperm M OS-525—were all developed based on FlexOS combined with X/GEM.

Furthermore, FlexOS was available on hardware like the Sicomp PC16-20 and PC32 computer series.

CTM

The shared terminal systems CTM III and CTM IV used by Japan Post were developed on the FlexOS platform.