FlexOS 68K

FlexOS
Company type	Operating system
Industry	Computer software
Predecessor	Concurrent DOS
Founded	1985; 41 years ago
Founder	Francis "Frank" R. Holsworth
Fate	Acquired by Integrated Systems Inc. in 1994; development ended after acquisition by Wind River Systems in 2000
Successor	IBM 4690 OS, Toshiba 4690 OS, Siemens S5-DOS/MT
Headquarters	Monterey, United States
Area served	Industrial, laboratory, retail, and financial sectors
Key people	Francis "Frank" R. Holsworth
Products	FlexOS operating system versions for Motorola 68000, Intel 80286, 80186, 80386, NEC V60 processors
Owner	Digital Research (until 1991), Novell (1991–1994), Integrated Systems Inc. (from 1994)
Parent	Digital Research, Novell, Integrated Systems Inc.

FlexOS was a modular real-time multitasking and multiuser operating system (RTOS) created by the Flexible Automation Business Unit of Digital Research in Monterey, California, in 1985. It was developed primarily for industrial, laboratory, retail, and financial sector applications.

As the successor to Digital Research's earlier Concurrent DOS, FlexOS introduced a redesigned modular structure and was engineered for portability across various processor architectures. Initially released under the names Concurrent DOS 68K and Concurrent DOS 286, it was rebranded as FlexOS on 1 October 1986 to clearly reflect its specialized market orientation.

Several original equipment manufacturers (OEMs) adopted FlexOS as the core platform for their proprietary operating systems, such as 4680 OS, 4690 OS, and S5-DOS/MT. Meanwhile, the original Concurrent DOS line continued to evolve independently with successors 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 (identified by the siglum FRH). Similar to Portable CP/M, these operating systems were programmed in C to facilitate hardware portability while delivering low interrupt latency and rapid context switching.

The initial protected mode release, FlexOS 286 version 1.3, targeted Intel 286 processors, with planned expansions for NEC V60, V70, and Motorola 68000 CPUs. Executable files for FlexOS 286 carried the .286 extension to indicate native API usage, complemented by a CP/M API front-end that supported .CMD files. The .68K extension denoted executables for FlexOS 68K, which originated from Concurrent DOS 68K.

In May 1987, version 1.31 of FlexOS was launched for systems based on the Intel 80286 architecture, requiring IBM PC/AT-compatible hardware equipped with 640 KB of conventional memory plus 512 KB of extended memory. This release introduced dynamically loadable subdrivers for devices such as floppy drives, hard disks, printers, serial ports, RAM disks, mice, and console interfaces.

During startup, the FLEX286.SYS kernel loaded resource managers and drivers specified within a binary CONFIG.SYS configuration file. Its command interpreter (COMMAND.286) executed a CONFIG.BAT batch script rather than the traditional AUTOEXEC.BAT. An optional DOS emulator provided limited compatibility with PC DOS 2.1 programs (.COM and .EXE) in protected mode; however, this required at least the Intel 80286 E2 stepping due to bugs in earlier CPU versions.

FlexOS also offered optional multitasking support through integration with the Graphics Environment Manager (GEM) Virtual Device Interface (VDI), enabling graphical application execution. Version 1.31 was capable of linking with GEM and included support for Novell's FlexNet networking technology.

By mid-1987, the FlexOS family expanded to include FlexOS 386 for host systems and FlexOS 186 tailored for remote controllers. The FlexOS 386 variant added windowing capabilities along with compatibility enhancements for PC DOS 3.2 and GEM environments. Versions 2.0 of both FlexOS 286 and FlexOS 386 were officially registered in July 1989.

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

In July 1991, Novell acquired Digital Research in an $80 million transaction. Subsequently, X/GEM version 1.0 for FlexOS and Novell's FlexNet were registered in December 1992. FlexOS also served as the principal testing platform for Novell Embedded Systems Technology (NEST).

Following Novell's decision to discontinue development on Digital Research operating systems like Multiuser DOS and Novell DOS products, it divested FlexOS to Integrated Systems Inc. (ISI) of Santa Clara in July 1994 for $3 million—half paid in cash and half through shares representing a two percent stake in ISI. ISI already maintained pSOS+, another modular real-time operating system targeting embedded platforms but continued supporting FlexOS after acquisition.

As of May 1998, FlexOS version 2.33 remained current; plans existed for version 2.34 to introduce support for faster processors, memory capacities up to 64 MB, Enhanced IDE (EIDE), and ATAPI CD-ROM drives. The acquisition of Integrated Systems by competitor Wind River Systems in February 2000 marked the conclusion of further development on both pSOS+ and FlexOS.

Commands

FlexOS offers an extensive array of commands, which include:

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 several hardware platforms, with multiple versions released:

Motorola 68000 / Freescale/NXP ColdFire MCF5251:

Concurrent DOS 68K 1.0 (1985)
Concurrent DOS 68K 1.1 and 1.20 (1986)
Concurrent DOS 68K 1.21 (1986)
FlexOS 68K 1.x (undated)

Intel 80286:

MP/M-286 (1982)
Concurrent CP/M-286 (1985)
Early preview of Concurrent DOS 286 (early 1985)
Concurrent DOS 286 series from version 1.0 to 1.2 (1985–1986)
FlexOS 286 iterations beginning with version 1.3 (November 1986) through to version 2.32 (July 1993)

Intel 80186 / NEC V20/V30:

FlexOS 186 branch initiated in September 1986, with the first release in June 1987

Intel 80386:

FlexOS 386 line starting at version 1.0 (June 1987) and extending up to planned releases including version 2.34 (1999), featuring key updates in July 1989 and May 1998

NEC V60:

Concurrent DOS V60 (dates unspecified)

These platform-specific editions demonstrate FlexOS’s approach to catering to a variety of hardware environments and evolving computing demands, supporting real-time multitasking and multiuser capabilities on major processor architectures.

IBM 4680 OS

In 1986, IBM chose DR Concurrent DOS 286 as the core for their IBM 4680 operating system, utilized in IBM Plant System products and Point-of-Sale terminals. The final iteration was Version 4 before transitioning to IBM's subsequent platform, IBM 4690 Version 1.

The releases encompassed:

IBM 4680 Operating System Version 1, Releases 1 through 3
Versions 2 Release 1, Version 3 Release 1, and Version 4 Release 1

IBM and Toshiba 4690 OS

IBM based IBM 4690 OS Version 1 on FlexOS version 2.32 in July 1993; it was initially previewed in September that year and became broadly accessible by March 1994. Compared to IBM 4680 OS Version 4, this iteration enhanced memory handling, console and pipe mechanisms, and overall system efficiency, eliminating previous constraints on simultaneous applications via optimized KOSPOOL utilization.

Subsequent IBM 4690 OS Version 2 introduced features such as Java support, long filename capabilities through a virtual filesystem (VFS), and compatibility with FAT32 volumes.

By mid-2005, IBM's POS register/client market share for IBM 4690 OS stood at approximately 12%, even as IBM started migrating users toward IBM Retail Environment for SUSE (IRES).

IBM continued supporting the operating system until April 2015; the most recent IBM update was Version 6 Release 3 issued in May 2012.

Meanwhile, Toshiba advanced development with Toshiba's own versions: Toshiba 4690 OS Version 6 Release 4 (January 2014) and Release 5 (January 2016).

Siemens S5-DOS/MT

Siemens integrates FlexOS within its factory automation solutions, particularly in the Simatic S5 STEP-5 platform, where the S5-DOS/MT variant is built upon FlexOS 386 combined with X/GEM, FlexNet, and Btrieve. The more compact S5-DOS traces its origins to Digital Research's Personal CP/M-86.

Additional Siemens industrial offerings such as COROS LS-B/FlexOS, COROS OS-B/FlexOS, and GRACIS/FlexOS also incorporate FlexOS alongside X/GEM.

FlexOS was supported on various Siemens computing hardware, including the SICOMP PC 16-20 and PC 32 product lines.

CTM

The shared terminal systems CTM III and CTM IV used by the Japanese postal service were developed based on FlexOS.