Concurrent DOS V60

FlexOS
Company type	Operating system
Industry	Computer software
Founded	1985; 41 years ago
Headquarters	Monterey, United States
Products	Real-time multitasking and multiuser operating system
Owner	Digital Research (original), Novell, Integrated Systems Inc., Wind River Systems

FlexOS was a modular, real-time multitasking and multiuser operating system (RTOS) that has since been discontinued. It was specifically engineered for applications in computer-integrated manufacturing, laboratory environments, retail sectors, and financial industries. The system was developed in 1985 by the Flexible Automation Business Unit of Digital Research, located in Monterey, California.

Initially created as a follow-up to Digital Research's earlier Concurrent DOS product, FlexOS introduced a modular design and was engineered for portability across various processor architectures. Its original designations were Concurrent DOS 68K and Concurrent DOS 286, but on 1 October 1986, it was rebranded as FlexOS to more clearly reflect its intended market segments.

Several original equipment manufacturers (OEMs) licensed FlexOS as the underlying platform for their proprietary operating systems, including 4680 OS, 4690 OS, and S5-DOS/MT. Meanwhile, the Concurrent DOS lineage continued independently through successors such as 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 (initials FRH). Similar to Portable CP/M, these operating systems were implemented in the C programming language to enhance hardware portability. They were designed with low interrupt latency and rapid context switching capabilities.

The initial protected mode iteration of FlexOS 286 (version 1.3) targeted Intel 286 processors, with future adaptations planned for NEC V60, NEC V70, and Motorola 68000 CPUs. Executable files for FlexOS 286 carried the .286 extension, while a CP/M API compatibility layer allowed execution of .CMD files. The .68K extension identified executables for FlexOS 68K, which was based on Concurrent DOS 68K.

In May 1987, version 1.31 of FlexOS was launched for machines powered by the Intel 80286 CPU. The development kit required an IBM PC/AT-compatible computer equipped with 640 KB of conventional memory and an additional 512 KB of extended memory, alongside CGA or EGA display adapters. FlexOS supported dynamically loadable subdrivers with predefined interfaces for devices such as floppy drives, hard disks, printers, serial ports, RAM disks, mice, and console terminals.

During system startup, the FLEX286.SYS kernel loaded resource managers and device drivers as configured in a binary CONFIG.SYS file; its command interpreter (COMMAND.286) executed a startup batch script named CONFIG.BAT instead of AUTOEXEC.BAT. An optional DOS emulator provided limited compatibility with PC DOS 2.1 programs (.COM and .EXE), running them within protected mode. This feature required at least an Intel 80286 E2 stepping processor due to earlier CPU errata.

FlexOS offered optional support for multitasking graphical applications through integration with the Graphics Environment Manager (GEM) Virtual Device Interface (VDI). Version 1.31 could be linked with GEM and included networking support via Novell's FlexNet.

By June 1987, FlexOS version 1.0 was available for both Intel 386 host systems and Intel 186-based remote controllers. The FlexOS 386 variant introduced windowing capabilities along with compatibility for PC DOS 3.2 and GEM. Versions 2.0 of both FlexOS 286 and FlexOS 386 were officially registered on July 3, 1989.

By the early 1990s (1990/1991), key clients included FANUC, IBM, ICL, Nixdorf, Siemens, Toshiba TEC, Thorn EMI Software, and Micrologic.

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

When Novell discontinued development of Digital Research operating systems such as Multiuser DOS and Novell DOS, it sold FlexOS to Integrated Systems Inc. (ISI), headquartered in Santa Clara, in July 1994 for $3 million—half paid upfront along with shares representing a two percent stake in ISI. ISI already maintained pSOS+, another real-time multitasking OS aimed at embedded systems but continued to support FlexOS after acquisition.

As of May 1998, the latest released version was FlexOS 2.33; plans existed for version 2.34 to introduce enhancements including support for faster processors, up to 64 MB RAM capacity, EIDE interfaces, and ATAPI CD-ROM drives. An improved version labeled 2.4 was also under consideration though its release status remains uncertain.

Integrated Systems was acquired by competitor Wind River Systems in February 2000; this acquisition effectively marked the end of ongoing development efforts for both pSOS+ and FlexOS.

Commands

FlexOS provides a variety of commands that are vital for managing system functions:

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 operate on various hardware platforms, with notable editions including:

Motorola 68000 / Freescale/NXP ColdFire MCF5251 platform:

Concurrent DOS 68K 1.0 released in 1985
Concurrent DOS 68K 1.1
Concurrent DOS 68K 1.20 launched in April 1986
Concurrent DOS 68K 1.21 issued in 1986
FlexOS 68K series in the 1.x range

Intel 80286 platform:

MP/M-286 introduced in 1982
Concurrent CP/M-286 from 1985
Concurrent DOS 286 preview and subsequent versions beginning in 1985, progressing through releases from 1.0 to 1.2 with incremental improvements
FlexOS 286 line starting at version 1.3 in November 1986 and advancing to version 2.32 by July 1993

Intel 80186/NEC V20/NEC V30 platform:

FlexOS 186 branch initiated in September 1986
Version 1.0 of FlexOS 186 launched June 1987

Intel 80386 platform:

FlexOS 386 debuted in June 1987 with updates continuing up to version 2.34 planned for release in 1999

NEC V60 platform:

A variant known as Concurrent DOS V60 was developed, though detailed information is scarce

This multi-platform strategy enabled FlexOS to serve a wide range of industries, delivering support for embedded and real-time systems while evolving alongside hardware innovations.

IBM 4680 OS

IBM developed the IBM 4680 system for Plant System products and Point-of-Sale terminals based on DR Concurrent DOS 286, releasing IBM 4680 OS Version 1 in 1986. The product line culminated with Version 4 before being succeeded by IBM 4690 OS Version 1.

The versions comprised:

IBM 4680 OS Version 1 Releases from 1 through 3
IBM 4680 OS Versions 2, 3, and 4 with their respective initial releases

IBM and Toshiba 4690 OS

In July of 1993, IBM selected FlexOS version 2.32 as the core for IBM's release of IBM 4690 OS Version 1, which was previewed in September that year and broadly available by March of the following year. Compared to IBM's prior system, IBM 4680 OS Version 4, FlexOS delivered enhanced memory handling, improved console and pipe mechanisms, and eliminated restrictions on the number of simultaneous applications.

IBM's subsequent release, IBM 4690 OS Version 2, incorporated support for the Java programming language, introduced long filename capabilities through a virtual filesystem (VFS), and enabled FAT32 volume compatibility.

By mid-2005, IBM's share of the point-of-sale register/client market using IBM 4690 OS remained at approximately twelve percent as IBM transitioned toward the IBM Retail Environment for SUSE (IRES).

IBM supported this platform until April of 2015; its final official release was Version 6 Release 3 issued in May 2012. Toshiba continued further development with Versions 6 Release 4 in January 2014 and Release 5 in January 2016.

Siemens S5-DOS/MT

Siemens employs FlexOS within its factory automation solutions. Notably, the Simatic S5 STEP-5 operating system, known as S5-DOS/MT, is constructed on FlexOS 386 and incorporates X/GEM, FlexNet, and Btrieve. The more compact S5-DOS version 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 also made use of FlexOS alongside X/GEM.

FlexOS was likewise available on hardware models including the PC 16-20 and PC 32 series.

CTM

The shared terminal systems CTM III and CTM IV, utilized by the Japanese postal service, were built upon FlexOS.