| FlexOS | DOS_386 | List_of_operating_systems | IBM_4690_OS | List_of_DOS_operating_systems | Comparison_of_executable_file_formats | Concurrent_DOS_386 | Digital_Research | List_of_real-time_operating_systems | Timeline_of_DOS_operating_systems | LOADALL | DOS_286 | Drive_letter_assignment | DOS | CONFIG.SYS | List_of_fictional_robots_and_androids |
|Company / developer||Digital Research|
|Latest stable release||2.33|
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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In May 1987, FlexOS version 1.31 was released for 80286 machines. The developer version required an 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, mice 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 batch job instead of the common AUTOEXEC.BAT.
FlexOS's 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.
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).
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.
When Novell decided to abandon further development of the various Digital Research operating systems such as 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 soon after with added support for faster CPUs, 64 MB of memory, EIDE and ATAPI CDROM drives.
Named IBM 4680 OS version 1, 
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. 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. Further, it removed limits on the number of applications running concurrently due to its more efficient use of KOSPOOL.
According to "The Year of the Store?", IHL Consulting Group/RIS News, IBM 4690 OS still had a market share of 12% in the POS register/client market in June 2005, when IBM was starting to phase it out in favour to IBM Retail Environment for SUSE (IRES).
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.