FlexOS was a modular real-time multi-user multi-tasking operating system (RTOS) designed for computer-integrated manufacturing, laboratory, retail and financial markets. It was developed by Digital Research's Flexible Automation Business Unit in Monterey, California since 1986 and was marketed since January 1987 as a derivation of Digital Research's Concurrent DOS 286 multiuser multitasking operating system.
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FlexOS was re-written in C for higher portability across hardware platforms, and it featured very low interrupt latency and fast context switching.[1]
The original protected mode FlexOS 286 version 1.0 was designed for host machines equipped with 286 CPUs, and with adaptions for NEC V60, NEC V70 and Motorola 68000 processors planned. FlexOS 286 executables using the system's native INT 220 application program interface had the file extension .286. A CP/M API front end (FE) was available as well.[2] (A file extension of .68K was reserved for FlexOS 68K, presumably derived from Concurrent DOS 68K as of 1986.[2])
In May 1987, FlexOS version 1.31 was released for 80286 machines. The developer version required a IBM PC/AT compatible machine with 640 KB of conventional and 512 KB of extended memory, and either a (monochrome) CGA or an EGA graphics adapter.
FlexOS supported a concept of dynamically loadable and unloadable subdrivers, and it came with driver prototypes for floppies, hard disks, printers, serial interfaces, RAM disks, mouses and console drivers.
During boot, the FLEX286.SYS kernel would load the resource managers and device drivers specified in the CONFIG.SYS binary file (not to be mixed up with the similarly named CONFIG.SYS configuration file under DOS), and its shell would execute a CONFIG.BAT startup batchjob instead of the common AUTOEXEC.BAT.
FlexOS' optional DOS emulator provided limited PC DOS 2.1 compatibility for DOS .COM and .EXE programs. Certain restrictions applied since these programs were executed in the processor's protected mode. Due to bugs in earlier steppings of the Intel 80286, the FlexOS 286 DOS front-end required at least the 80286 E2 stepping to function properly. These problems had already caused delays in the delivery of Concurrent DOS 286 earlier.[3][4]
The system optionally supported a multitasking GEM VDI for graphical applications.
FlexOS 1.31 could be linked with none, either or both of these two modules. FlexOS 1.31 also supported FlexNet.
By June 1987 there were also versions 1.0 of FlexOS 386 (for hosts) and FlexOS 186 (for remote cell controllers).[1]
FlexOS 286 and FlexOS 386 versions 2.0 were registered on 3 July 1989.
Novell bought Digital Research in July 1991.
X/GEM for FlexOS release 1.0 (aka X/GEM FlexOS 286 and 386) and FlexNet were registered on 21 December 1992.
FlexOS was used as the primary test platform for the new Novell Embedded Systems Technology (NEST).[5]
When Novell decided to abandon further development of the various Digital Research operating systems such as Multiuser DOS (a successor to Concurrent DOS) and Novell DOS (a successor to DR DOS), they sold FlexOS off to the Santa Clara, California-based Integrated Systems, Inc. (ISI) for US$3,000,000 in July 1994. The deal comprised a direct payment of half this sum as well as shares representing 2% of the company. The company already had pSOS+, another modular real-time multitasking operating system for embedded systems, but they continued to maintain FlexOS as well. FlexOS version 2.33 was current as of May 1998 and with FlexOS 2.34 to be released soonafter with added support for faster CPUs, 64 MB of memory, EIDE and ATAPI CDROM drives.
Integrated Systems was bought by their competitor Wind River Systems in 1999.
Named IBM 4680 OS version 1, IBM originally chosed DR Concurrent DOS 286 as the basis of their IBM 4680 computer for IBM Plant System products and Point-of-Sale terminals in 1986.[2][6] The last release of the IBM 4680 OS has been version 4, before it was replaced by IBM 4690 version 1.[7]
In July 1993, IBM announced the adoption of FlexOS version 2.32 as the basis of their IBM 4690 OS version 1, to be pre-released on 24 September 1993 and generally made available from 25 March 1994.[7][8] FlexOS 2.32 supported 286 and 386 modes, had more efficient memory management, better console and pipe systems, and brought overall quality and performance improvements compared to the version that came with IBM 4680 OS version 4.[7] Further, it removed limits on the number of applications running concurrently due to its more efficient use of KOSPOOL.[7]
IBM continues to maintain their 4690 OS up to the present, with the most recent version in April 2010 being IBM 4690 OS version 6.2.
Siemens used and still maintains FlexOS in their factory automation equipment as well. For example, their Simatic S5 STEP-5 operating system S5-DOS/MT is based on FlexOS 386 with X/GEM, FlexNet and Btrieve, whereas the smaller S5-DOS system, also present on these systems, is a variant of Digital Research's Personal CP/M-86.