FlexOS

FlexOS
Company type	Operating system
Industry	Software, Embedded systems
Founded	1985
Founder	Digital Research's Flexible Automation Business Unit
Headquarters	Monterey, United States
Products	FlexOS operating system

FlexOS was a modular, real-time multitasking operating system designed for multiple users, developed by Digital Research's Flexible Automation Business Unit in Monterey, California, and introduced in 1985. It was aimed primarily at sectors such as industrial automation, retail environments, and financial services, including applications like computer-integrated manufacturing and point-of-sale systems.

Conceived as the successor to Digital Research's earlier Concurrent DOS, FlexOS introduced a fresh modular design and was engineered to be portable across various processor architectures. Originally released 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 licensed FlexOS to build their proprietary operating systems, examples being 4680 OS, 4690 OS, and S5-DOS/MT. Meanwhile, the Concurrent DOS lineage continued independently with successors such as Concurrent DOS XM and Concurrent DOS 386.

Overview

The designs of Concurrent DOS 286, Concurrent DOS 68K, and FlexOS were attributed to Francis "Frank" R. Holsworth (signature FRH). Similar to Portable CP/M and other Digital Research products like Concurrent DOS V60, these systems were developed in the C programming language to ensure cross-platform portability. They featured characteristics such as minimal interrupt latency and rapid context switching.

FlexOS version 1.3 for the Intel 286 processor operated in protected mode and was intended for the Intel 286 CPU family, with planned versions for NEC V60, NEC V70, and Motorola 68000 processors. Executables for FlexOS 286 that utilized the native INT DCh (INT 220) API bore the .286 file extension; those using a CP/M API interface had .CMD extensions. The .68K extension identified FlexOS 68K binaries, which evolved from Concurrent DOS 68K beginning in 1986.

In May 1987, version 1.31 of FlexOS was launched for machines based on the Intel 80286 architecture. The development environment required an IBM PC/AT-compatible system equipped with 640 KB of conventional memory alongside 512 KB of extended memory and supported CGA or EGA display adapters.

FlexOS featured dynamically loadable subdrivers and provided sample drivers for devices including floppy drives, hard disks, printers, serial ports, RAM disks, mice, and console interfaces. At startup, the FLEX286.SYS kernel loaded resource managers and device drivers as specified within a binary CONFIG.SYS configuration file; its command interpreter (COMMAND.286) ran a CONFIG.BAT batch script instead of AUTOEXEC.BAT during boot.

An optional DOS emulator offered limited compatibility with PC DOS 2.1 programs (.COM and .EXE) executing in protected mode. Early stepping bugs in Intel’s 80286 CPU necessitated at least an E2 stepping revision for proper operation of this DOS front-end—a factor that had previously delayed delivery of Concurrent DOS 286.

FlexOS optionally supported multitasking through the Graphics Environment Manager (GEM) Virtual Device Interface (VDI), enabling graphical applications. Version 1.31 could link with zero, one, or both modules and included support for Novell’s FlexNet networking system.

By June 1987, FlexOS versions targeting different platforms were available: FlexOS 386 for host systems and FlexOS 186 for remote controllers. FlexOS 386 introduced windowing capabilities along with compatibility for PC DOS 3.2 and GEM environments.

Copyright registrations for FlexOS versions 2.0 of both the 286 and 386 editions were filed on July 3, 1989.

Key clients around 1990–1991 included companies 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 for FlexOS release 1.0—also known as X/GEM FlexOS 286 and X/GEM FlexOS 386—and FlexNet were registered on December 21, 1992.

FlexOS functioned as the main development platform for Novell Embedded Systems Technology (NEST).

When Novell discontinued further development of Digital Research operating systems like 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 with shares representing a two percent holding in ISI. ISI already owned pSOS+, another modular real-time multitasking OS designed for embedded applications but continued supporting FlexOS after acquisition.

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

Integrated Systems was purchased by Wind River Systems in February 2000; this acquisition effectively terminated further advancements of both pSOS+ and FlexOS operating systems.

Commands

FlexOS offers 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 to run on various CPU architectures, demonstrating its versatility across different commercial sectors:

Motorola 68000 / Freescale/NXP ColdFire MCF5251 platform:

Concurrent DOS 68K series from version 1.0 in 1985 up to 1.21 in 1986
FlexOS 68K series with versions in the 1.x range

Intel 80286 platform:

MP/M-286 launched in 1982
Concurrent CP/M-286 and Concurrent DOS 286 iterations, starting with a preview release in 1985 through to version 1.2.02 in 1986
FlexOS 286 editions from version 1.3 released in November 1986 through to version 2.32 issued in July 1993

Intel 80186/NEC V20/NEC V30 platform:

Initial FlexOS 186 release debuted in June 1987

Intel 80386 platform:

FlexOS 386 editions spanning from version 1.0 in June 1987, with planned updates extending into the late 1990s, including release 2.34

NEC V60 platform:

Variant known as Concurrent DOS V60

These diverse releases highlight FlexOS's deliberate approach to addressing emerging microprocessor markets, focusing on sectors that require real-time multitasking capabilities and modular OS design.

IBM 4680 OS

In 1986, IBM chose DR Concurrent DOS 286 as the core technology for their IBM 4680 operating system, which powered IBM Plant System equipment and various Point-of-Sale terminals. The system evolved through several iterations, culminating with Version 4 before transitioning to IBM 4690 OS Version 1.

The released versions included:

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 of 1993, IBM adopted FlexOS version 2.32 as the foundation for the initial release of the IBM 4690 OS, which was pre-launched in September and became widely available by March of the following year. This iteration enhanced memory handling, improved console and pipe functionalities, and boosted overall system efficiency compared to IBM's prior version, the IBM 4680 OS Version 4. It also eliminated restrictions on simultaneous applications by leveraging an optimized KOSPOOL mechanism.

Subsequent updates included IBM 4690 OS Version 2, which introduced Java compatibility along with a virtual filesystem architecture supporting long filenames and FAT32 volume management.

By mid-2005, the IBM 4690 OS held approximately a twelve percent share of the Point-of-Sale register market; however, IBM began transitioning away from it toward the IBM Retail Environment for SUSE (IRES). The operating system was officially supported until April of 2015, with the latest IBM-issued update being Version 6 Release 3 in May of 2012.

Meanwhile, Toshiba continued advancing the platform with releases such as Version 6 Release 4 in January 2014 and Release 5 in January 2016.

Siemens S5-DOS/MT

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

Additional Siemens industrial platforms, including COROS LS-B/FlexOS, COROS OS-B/FlexOS, and GRACIS/FlexOS, also employ FlexOS combined with X/GEM.

FlexOS was available as an optional operating system on computer models like the PC16-20 and PC32 series.

CTM

Japan Post utilized FlexOS as the foundation for its shared terminal systems, specifically the CTM III and CTM IV models.