FlexOS 386

FlexOS
Company type	Software
Industry	Operating systems
Predecessor	Concurrent DOS
Founded	1985
Headquarters	Monterey, California, United States
Products	Real-time operating system (RTOS)
Owner	Digital Research (original), Novell (after 1991), Integrated Systems Inc. (after 1994)

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

Conceived as the successor to Digital Research's earlier Concurrent DOS, FlexOS introduced a fresh modular design and was engineered for portability across various processor architectures. Initially known under the names Concurrent DOS 68K and Concurrent DOS 286, it was renamed FlexOS on October 1, 1986, to better reflect its specialized market positioning.

Several original equipment manufacturers (OEMs) licensed FlexOS as the base for their proprietary operating systems, including 4680 OS, 4690 OS, and S5-DOS/MT. Meanwhile, the original Concurrent DOS lineage continued independently with successors such as Concurrent DOS XM and Concurrent DOS 386.

Overview

The design of Concurrent DOS 286, Concurrent DOS 68K, and FlexOS was led by Francis "Frank" R. Holsworth (signature FRH). Similar to Portable CP/M, these operating systems—including Concurrent DOS V60—were implemented in C to facilitate hardware platform portability. They were optimized for minimal interrupt latency and rapid context switching.

The initial protected mode release of FlexOS 286 version 1.3 targeted Intel 286 processors, with planned versions for NEC V60, NEC V70, and Motorola 68000 CPUs. Executable files for FlexOS 286 carried the .286 extension and utilized the system’s native INT DCh (INT 220) API. A CP/M-compatible API front-end was provided through files with the .CMD extension. The .68K extension was reserved for FlexOS 68K, which evolved from Concurrent DOS 68K starting in 1986.

In May 1987, version 1.31 of FlexOS became available for machines based on the Intel 80286 processor. The development environment required an IBM PC/AT-compatible system equipped with at least 640 KB of conventional memory and 512 KB of extended memory, along with CGA or EGA graphics adapters.

FlexOS featured dynamically loadable subdrivers supporting devices such as floppy drives, hard disks, printers, serial ports, RAM disks, mice, and console interfaces. During system startup, the FLEX286.SYS kernel loaded resource managers and device drivers defined within a binary CONFIG.SYS file; its command interpreter (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 applications (.COM and .EXE files) running under protected mode. This emulator required at least an Intel 80286 E2 stepping CPU due to earlier processor errata that delayed the release of Concurrent DOS 286.

FlexOS optionally supported multitasking through integration with the Graphics Environment Manager (GEM) Virtual Device Interface (VDI), enabling graphical application support. Version 1.31 of FlexOS could be linked with GEM and also supported Novell’s FlexNet networking system.

By June 1987, FlexOS versions targeting the Intel 386 (host systems) and Intel 186 (remote controllers) were released; FlexOS 386 introduced windowing capabilities alongside compatibility with PC DOS 3.2 and GEM. Subsequent versions 2.0 for both FlexOS 286 and 386 were officially registered on July 3, 1989.

Notable clients during the period of 1990–1991 included FANUC, IBM, ICL, Nixdorf, Siemens, Toshiba TEC, Thorn EMI Software, and Micrologic.

In July 1991, Novell acquired Digital Research for $80 million. Later that year in December 1992, X/GEM for FlexOS release 1.0 along with FlexNet were registered trademarks. FlexOS also served as Novell’s main testing platform for Novell Embedded Systems Technology (NEST).

Following Novell’s decision to discontinue development of Digital Research operating systems such as Multiuser DOS and Novell DOS, it sold FlexOS to Integrated Systems Inc. (ISI), based in Santa Clara, in July 1994 for $3 million—half paid in cash and half in ISI shares representing a two percent stake. ISI continued supporting FlexOS alongside its pSOS+ real-time operating system.

As of May 1998, FlexOS version 2.33 remained current; version 2.34 introduced enhancements including support for faster processors up to a maximum of 64 MB RAM as well as EIDE and ATAPI CD-ROM devices. Although plans for a significant update labeled version 2.4 existed, its actual release remains uncertain.

Integrated Systems was acquired by Wind River Systems in February 2000; this acquisition marked the end of further development efforts on both pSOS+ and FlexOS platforms.

Commands

FlexOS provides a variety of commands that are vital for the system's functionality and administration:

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 to run on several hardware platforms, with key releases including:

Motorola 68000 / Freescale/NXP ColdFire MCF5251 platform:

Concurrent DOS 68K 1.0 launched in 1985
Concurrent DOS 68K 1.1
Concurrent DOS 68K 1.20 through 1.21 issued in 1986
FlexOS 68K series, version 1.x

Intel 80286 platform:

MP/M-286 debuted in 1982
Concurrent CP/M-286 released in 1985
Multiple Concurrent DOS 286 editions from preview to final versions between 1985 and 1986, spanning releases from 1.0 to 1.2.02
FlexOS 286 editions beginning with version 1.3 in 1986 and continuing up to version 2.32 in 1993

Intel 80186/NEC V20/NEC V30 platform:

FlexOS 186 branch initiated in 1986, with the initial release version 1.0 appearing in June 1987

Intel 80386 platform:

FlexOS 386 series starting at version 1.0 in June 1987, with plans for subsequent releases including version 2.34 projected for 1999

NEC V60 platform:

Concurrent DOS V60 adaptation

These editions demonstrate FlexOS’s versatility across changing microprocessor designs, meeting a variety of business computing requirements over time.

IBM 4680 OS

Initially, IBM based their IBM 4680 operating system for Plant System hardware and Point-of-Sale terminals on DR Concurrent DOS 286 in the year 1986, naming it IBM 4680 OS Version 1. The final iteration released was Version 4 before transitioning to IBM's subsequent IBM 4690 Version 1.

The versions comprised:

IBM 4680 OS Version 1 Release levels from Release 1 through Release 3
IBM 4680 OS Versions 2, 3, and the first release of Version 4

IBM and Toshiba 4690 OS

In July of 1993, IBM selected FlexOS version 2.32 as the base for IBM’s new IBM 4690 OS Version 1, which was previewed in September and widely distributed starting March 1994. Compared to IBM 4680 OS Version 4, FlexOS 2.32 improved memory handling, console and pipe mechanisms, and overall system efficiency by eliminating concurrent application restrictions via enhanced KOSPOOL utilization.

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

By mid-2005, IBM 4690 OS commanded approximately a twelve percent share of the Point of Sale register/client market, even as IBM began shifting toward the IBM Retail Environment for SUSE (IRES).

IBM continued maintaining this operating system until April 2015; the most recent IBM update was Version 6 Release 3 issued in May 2012. Toshiba advanced development further with Versions 6 Release 4 released in January 2014 and Release 5 issued in January 2016.

Siemens S5-DOS/MT

Siemens integrates FlexOS within its industrial automation solutions. The operating system for their Simatic S5 series, known as S5-DOS/MT, is constructed upon FlexOS 386 and incorporates X/GEM, FlexNet, and Btrieve. Meanwhile, the more compact S5-DOS traces its origins to Digital Research's Personal CP/M-86.

Additional Siemens industrial platforms such as COROS LS-B/FlexOS, COROS OS-B/FlexOS, GRACIS/FlexOS, and OS-525 are also built using FlexOS alongside X/GEM.

FlexOS was offered as an operating system option on hardware like the PC 16-20 and PC 32 computer lines.

CTM

The shared terminal systems CTM III and CTM IV used by Japan's postal service were developed based on the FlexOS platform.