4680 Operating System

FlexOS
Company type	Operating system
Industry	Software, Operating systems
Predecessor	Concurrent DOS
Founded	1985
Headquarters	Monterey, California, United States
Products	Real-time operating system (RTOS)
Owner	Digital Research (until 1994), Integrated Systems Inc. (from 1994), Wind River Systems (from 2000)

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

Created as the successor to Digital Research's earlier Concurrent DOS, FlexOS featured a novel modular design that allowed it to be portable across various processor architectures. Originally known as Concurrent DOS 68K and Concurrent DOS 286, the system was rebranded as FlexOS on October 1, 1986, to more clearly reflect its targeted markets.

Multiple original equipment manufacturers (OEMs) licensed FlexOS to build their own platforms, such as 4680 OS, 4690 OS, and S5-DOS/MT. Meanwhile, the original Concurrent DOS lineage advanced independently with releases like Concurrent DOS XM and Concurrent DOS 386.

Overview

Francis "Frank" R. Holsworth (using the initials FRH) designed Concurrent DOS 286, Concurrent DOS 68K, and FlexOS. Similar to Portable CP/M, these systems—including Concurrent DOS V60—were implemented in C to ensure hardware portability while delivering low interrupt latency and rapid context switching.

The initial protected mode release, FlexOS 286 version 1.3, was tailored for Intel 286 processors, with planned versions for NEC V60, NEC V70, and Motorola 68000 CPUs. Executable files for FlexOS 286 utilized the native INT DCh (INT 220) API with a .286 suffix; there was also a CP/M API compatibility layer supporting .CMD files. Executables for FlexOS 68K—originating from Concurrent DOS 68K—carried the .68K extension as of 1986.

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

FlexOS incorporated dynamically loadable subdrivers covering devices such as floppy and hard disks, printers, serial ports, RAM disks, mice, and consoles. During startup, the FLEX286.SYS kernel loaded resource managers and device drivers specified within a binary CONFIG.SYS configuration file; its command interpreter (COMMAND.286) ran a CONFIG.BAT batch script instead of the traditional AUTOEXEC.BAT.

An optional DOS emulator provided limited compatibility with PC DOS 2.1 for .COM and .EXE applications by operating in protected mode under certain constraints. Due to hardware bugs in early Intel 80286 processors, this DOS compatibility layer required at least an E2 stepping CPU to function correctly—a limitation that had previously impacted Concurrent DOS 286.

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

By mid-1987, FlexOS variants included FlexOS 386 designed for host computers and FlexOS 186 aimed at remote cell controllers. The FlexOS 386 release introduced windowing capabilities alongside compatibility with PC DOS 3.2 and GEM.

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

Key clients around 1990–1991 comprised 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 (covering both X/GEM FlexOS 286 and 386) along with FlexNet were registered on December 21, 1992. FlexOS also served as the main testing platform for Novell Embedded Systems Technology (NEST).

Following Novell’s discontinuation of Digital Research OS products such as Multiuser DOS and Novell DOS, it sold FlexOS in July 1994 to Integrated Systems Inc. (ISI), based in Santa Clara, for $3 million—half paid in cash and half in company stock representing a two percent equity stake. ISI continued development of both their existing pSOS+ real-time operating system and FlexOS.

As of May 1998, version 2.33 of FlexOS remained current; version 2.34 was under development to support faster processors, increased memory capacity up to 64 MB, EIDE interfaces, and ATAPI CD-ROM drives. Plans were also underway for a substantially enhanced version 2.4 though its release status is uncertain.

In February 2000 Integrated Systems was acquired by competitor Wind River Systems, which subsequently terminated further development on both pSOS+ and FlexOS.

Commands

FlexOS offers support for a variety of commands, including the following:

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 principal versions including:

Motorola 68000 / Freescale /NXP ColdFire MCF5251 architecture:

Concurrent DOS 68K 1.0 released in 1985
Concurrent DOS 68K 1.1
Concurrent DOS 68K 1.20 issued in April 1986
Concurrent DOS 68K 1.21 from 1986
FlexOS 68K series marked as 1.x?

Intel 80286 architecture:

MP/M-286 debuting in 1982
Concurrent CP/M-286 launched in 1985
Concurrent DOS 286 offered preview and releases between 1985 and 1986, covering versions from 1.0 up to 1.2.02
FlexOS 286 editions ranging from version 1.3 introduced in November 1986 through to version 2.32 released by July 1993, with significant updates in the years 1987, 1988, and 1989

Intel 80186 /NEC V20 /NEC V30 architecture:

The FlexOS 186 branch originated in September 1986
FlexOS 186 version 1.0 launched in June 1987

Intel 80386 architecture:

The FlexOS 386 line began with version 1.0 in June 1987
Follow-up versions include release 2.0 in July 1989 and further revisions planned through to version 2.34 by 1999

NEC V60 architecture:

A variant known as Concurrent DOS V60

These diverse releases demonstrate FlexOS's versatility across different hardware systems, targeting enterprises requiring real-time multitasking operating environments.

IBM 4680 OS

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

The releases encompassed:

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

IBM and Toshiba 4690 OS

In July of 1993, IBM adopted FlexOS version 2.32 as the foundation for IBM’s release of the IBM 4690 OS Version 1, which became generally available in March 1994. This iteration enhanced memory handling, console and pipe mechanisms, and overall system efficiency compared to IBM 4680 OS Version 4, removing restrictions on concurrent applications by leveraging an improved KOSPOOL.

IBM introduced Java compatibility, support for long filenames via a virtual filesystem (VFS), and FAT32 volume handling with IBM 4690 OS Version 2.

By June 2005, the IBM 4690 OS maintained approximately a twelve percent share of the POS register/client marketplace, even as IBM initiated a phase-out in favor of the IBM Retail Environment for SUSE (IRES).

IBM continued supporting this platform until April 2015; the latest IBM-issued update was Version 6 Release 3 in May 2012. Toshiba carried forward development with Versions 6 Release 4 issued in January 2014 and Release 5 released in January 2016.

Siemens S5-DOS/MT

Siemens integrates FlexOS within its factory automation solutions. The operating system for their Simatic S5 line, known as S5-DOS/MT, is constructed upon FlexOS 386 and incorporates components such as X/GEM, FlexNet, and Btrieve. A more compact version, S5-DOS, originates from Digital Research's Personal CP/M-86.

Additional Siemens industrial platforms like COROS LS-B/FlexOS, COROS OS-B/FlexOS, and GRACIS/FlexOS also utilize FlexOS alongside X/GEM. Furthermore, machines in the Sicomp PC range operated using FlexOS.

CTM

Japan's postal service deployed shared terminal systems named CTM III and CTM IV, both developed on the FlexOS foundation.