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70-446: FlexOS is a discontinued modular real-time multiuser multitasking operating system ( RTOS ) designed for computer-integrated manufacturing, laboratory, retail and financial markets. Developed by Digital Research 's Flexible Automation Business Unit in Monterey , California, in 1985. The system was considered to become a successor of Digital Research's earlier Concurrent DOS , but with

140-435: A swap file or swap partition is a way for the operating system to provide more memory than is physically available by keeping portions of the primary memory in secondary storage . While multitasking and memory swapping are two completely unrelated techniques, they are very often used together, as swapping memory allows more tasks to be loaded at the same time. Typically, a multitasking system allows another process to run when

210-461: A Program Distributor feeding up to twenty-five autonomous processing units with code and data, and allowing concurrent operation of multiple clusters. Another such computer was the LEO III , first released in 1961. During batch processing , several different programs were loaded in the computer memory, and the first one began to run. When the first program reached an instruction waiting for a peripheral,

280-559: A Y2K compliant DOS. As it reports itself as "IBM PC-DOS 7 Revision 1", it is often refereed to as "IBM PC-DOS7R1" or just "PC-DOS7R1". Hitachi used PC DOS 2000 in their legacy Drive Fitness Test (4.15) and Hitachi Feature Tool (2.15) until 2009. ThinkPad products had a copy of the latest version of PC DOS in their Rescue and Recovery partition. PC DOS 7.1 added support for Logical Block Addressing (LBA) and FAT32 partitions. Various builds from 1999 up to 2003 were not released in retail, but used in products such as

350-465: A computer's memory, allowing the CPU to switch between them swiftly. This optimizes CPU utilization by keeping it engaged with the execution of tasks, particularly useful when one program is waiting for I/O operations to complete. The Bull Gamma 60 , initially designed in 1957 and first released in 1960, was the first computer designed with multiprogramming in mind. Its architecture featured a central memory and

420-487: 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 soon after with added support for faster CPUs, 64 MB of memory, EIDE and ATAPI CDROM drives. Integrated Systems

490-505: A few glitches. Newly added EMS drivers were only compatible with IBM's EMS boards and not the more common Intel and AST ones. DOS 4.0 is also notable for including the first version of the DOS Shell , a full-screen utility designed to make the command-line OS more user-friendly. Microsoft took back control of development and released a bug-fixed DOS 4.01. DOS 5 debuted in June 1991. DOS 5 supported

560-619: A group of Microsoft programmers (primarily Paul Allen , Mark Zbikowski and Aaron Reynolds ) began work on PC DOS 2.0. Completely rewritten, DOS 2.0 added subdirectories and hard disk support for the new IBM XT , which debuted in March 1983. A new 9-sector format bumped the capacity of floppy disks to 360 KB. The Unix -inspired kernel featured file handles in place of the CP/M-derivative file control blocks and loadable device drivers could now be used for adding hardware beyond that which

630-729: 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 continued to maintain 4690 OS up to April 2015, with the most recent version released by IBM in May 2012 being IBM 4690 OS Version 6 Release 3. Toshiba released Toshiba 4690 OS Version 6 Release 4 in January 2014 and Version 6 Release 5 in January 2016. 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

700-435: A new, modular, and considerably different system architecture and portability across several processor families. Still named Concurrent DOS 68K and Concurrent DOS 286 , it was renamed into FlexOS on 1 October 1986 to better differentiate the target audiences. FlexOS was licensed by several OEMs who selected it as the basis for their own operating systems like 4680 OS , 4690 OS , S5-DOS/MT and others. Unrelated to FlexOS,

770-523: A program will run in a timely manner. Indeed, the first program may very well run for hours without needing access to a peripheral. As there were no users waiting at an interactive terminal, this was no problem: users handed in a deck of punched cards to an operator, and came back a few hours later for printed results. Multiprogramming greatly reduced wait times when multiple batches were being processed. Early multitasking systems used applications that voluntarily ceded time to one another. This approach, which

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840-513: A series of suits on this, and so we didn't want to have a product which was clearly someone else's product worked on by IBM people. We went to Microsoft on the proposition that we wanted this to be their product. IBM first contacted Microsoft to look the company over in July 1980. Negotiations continued over the months that followed, and the paperwork was officially signed in early November. Although IBM expected that most customers would use PC DOS,

910-466: A single processor might be shared between calculations of machine movement, communications, and user interface. Often multitasking operating systems include measures to change the priority of individual tasks, so that important jobs receive more processor time than those considered less significant. Depending on the operating system, a task might be as large as an entire application program, or might be made up of smaller threads that carry out portions of

980-476: A standard 1.44 MB floppy disk to 1.86 MB. SuperStor disk compression technology was replaced with Stac Electronics ' STACKER . An algebraic command line calculator and a utility program to load device drivers from the command line were added. PC DOS 7 also included many optimizations to increase performance and reduce memory usage. The most recent retail release was PC DOS 2000 – released from Austin in 1998 – which found its niche in

1050-500: A variant to threads, named fibers , that are scheduled cooperatively. On operating systems that do not provide fibers, an application may implement its own fibers using repeated calls to worker functions. Fibers are even more lightweight than threads, and somewhat easier to program with, although they tend to lose some or all of the benefits of threads on machines with multiple processors . Some systems directly support multithreading in hardware . Essential to any multitasking system

1120-506: A windowing feature, and offered PC DOS 3.2 and GEM compatibility. FlexOS 286 and FlexOS 386 versions 2.0 were registered on 3 July 1989. Among the major FlexOS customers in 1990/1991 were FANUC , IBM , ICL , Nixdorf , Siemens , TEC , Thorn EMI Software and Micrologic . Novell bought Digital Research for US$ 80 million in July 1991. X/GEM for FlexOS release 1.0 (a.k.a. X/GEM FlexOS 286 and 386) and FlexNet were registered on 21 December 1992. FlexOS

1190-410: Is a common feature of computer operating systems since at least the 1960s. It allows more efficient use of the computer hardware; when a program is waiting for some external event such as a user input or an input/output transfer with a peripheral to complete, the central processor can still be used with another program. In a time-sharing system, multiple human operators use the same processor as if it

1260-496: Is a discontinued disk operating system for the IBM Personal Computer , its successors, and IBM PC compatibles . It was manufactured and sold by IBM from the early 1980s into the 2000s. Developed by Microsoft , it was also sold by that company as MS-DOS . Both operating systems were identical or almost identical until 1993, when IBM began selling PC DOS 6.1 with new features. The collective shorthand for PC DOS and MS-DOS

1330-454: 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 . Siemens industrial systems like COROS LS-B/FlexOS, COROS OS-B/FlexOS, GRACIS/FlexOS, Teleperm M  [ de ] OS-525 were FlexOS and X/GEM-based. Computers such as the Sicomp  [ de ] PC 16-20 and

1400-400: Is still used today on RISC OS systems. As a cooperatively multitasked system relies on each process regularly giving up time to other processes on the system, one poorly designed program can consume all of the CPU time for itself, either by performing extensive calculations or by busy waiting ; both would cause the whole system to hang . In a server environment, this is a hazard that makes

1470-400: Is to safely and effectively share access to system resources. Access to memory must be strictly managed to ensure that no process can inadvertently or deliberately read or write to memory locations outside the process's address space. This is done for the purpose of general system stability and data integrity, as well as data security. In general, memory access management is a responsibility of

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1540-659: The Classic Mac OS . In 2001 Apple switched to the NeXTSTEP -influenced Mac OS X . A similar model is used in Windows 9x and the Windows NT family , where native 32-bit applications are multitasked preemptively. 64-bit editions of Windows, both for the x86-64 and Itanium architectures, no longer support legacy 16-bit applications, and thus provide preemptive multitasking for all supported applications. Another reason for multitasking

1610-550: The IBM PC Convertible , IBM's first computer to use 3 + 1 ⁄ 2 -inch floppy disks, released April 1986, and later the IBM Personal System/2 in 1987. In June 1985, IBM and Microsoft signed a long-term Joint Development Agreement to share specified DOS code and create a new operating system from scratch, known at the time as Advanced DOS. On 2 April 1987 OS/2 was announced as the first product produced under

1680-544: The Intel 80286 -derived IBM PC/AT , its next-generation machine. Along with this was DOS 3.00. Despite jumping a whole version number, it again proved little more than an incremental upgrade, adding nothing more substantial than support for the AT's new 1.2 megabyte (MB) floppy disks. Planned networking capabilities in DOS 3.00 were judged too buggy to be usable and Microsoft disabled them prior to

1750-474: The Sinclair QL followed in 1984, but it was not a big success. Commodore's Amiga was released the following year, offering a combination of multitasking and multimedia capabilities. Microsoft made preemptive multitasking a core feature of their flagship operating system in the early 1990s when developing Windows NT 3.1 and then Windows 95 . In 1988 Apple offered A/UX as a UNIX System V -based alternative to

1820-411: The embedded software market and elsewhere. PC DOS 2000 is a slipstream of 7.0 with Y2K and other fixes applied. To applications, PC DOS 2000 reports itself as "IBM PC DOS 7.00, revision 1", in contrast to the original PC DOS 7, which reported itself as "IBM PC DOS 7.00, revision 0". PC-DOS 2000 was the last version of IBM PC-DOS that was sold at retail. IBM advertised it as

1890-429: The CPU (" CPU bound "). In primitive systems, the software would often " poll ", or " busywait " while waiting for requested input (such as disk, keyboard or network input). During this time, the system was not performing useful work. With the advent of interrupts and preemptive multitasking, I/O bound processes could be "blocked", or put on hold, pending the arrival of the necessary data, allowing other processes to utilize

1960-555: The CPU. As the arrival of the requested data would generate an interrupt, blocked processes could be guaranteed a timely return to execution. Possibly the earliest preemptive multitasking OS available to home users was Microware 's OS-9 , available for computers based on the Motorola 6809 such as the TRS-80 Color Computer 2 , with the operating system supplied by Tandy as an upgrade for disk-equipped systems. Sinclair QDOS on

2030-630: 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 (COMMAND.286) 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 in " 8086 emulation mode " since these programs were executed in

2100-471: The IBM PC BIOS supported. BASIC and most of the utilities provided with DOS were substantially upgraded as well. A major undertaking that took almost 10 months of work, DOS 2.0 was more than twice as big as DOS 1.x, occupying around 28 KB of RAM compared to the 12 KB of its predecessor. It would form the basis for all Microsoft consumer-oriented OSes until 2001, when Windows XP (based on Windows NT )

2170-448: The IBM PC also supported CP/M-86 , which became available six months after PC DOS, and UCSD p-System operating systems. IBM's expectation proved correct: one survey found that 96.3% of PCs were ordered with the $ 40 PC DOS compared to 3.4% with the $ 240 CP/M-86. Over the history of IBM PC DOS, various versions were developed by IBM and Microsoft. By the time PC DOS 3.0

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2240-660: The IBM PC an industry standard. Microsoft , founded five years earlier by Bill Gates , was eventually selected for the operating system. IBM wanted Microsoft to retain ownership of whatever software it developed, and wanted nothing to do with helping Microsoft, other than making suggestions from afar. According to task force member Jack Sams : The reasons were internal. We had a terrible problem being sued by people claiming we had stolen their stuff. It could be horribly expensive for us to have our programmers look at code that belonged to someone else because they would then come back and say we stole it and made all this money. We had lost

2310-519: The IBM PC. The initial version of DOS was largely based on CP/M-80 1.x and most of its architecture, function calls and file-naming conventions were copied directly from the older OS. The most significant difference was the fact that it introduced a different file system, FAT12 . Unlike all later DOS versions, the DATE and TIME commands were separate executables rather than part of COMMAND.COM . Single-sided 160 kilobyte (KB) 5.25-inch floppies were

2380-698: The IBM ServerGuide Scripting Toolkit. A build of this version of DOS appeared in Norton Ghost from Symantec . Version 7.1 indicates support for FAT32 also in MS-DOS . Most builds of this version of DOS are limited to the kernel files IBMBIO.COM , IBMDOS.COM , and COMMAND.COM . The updated programs FDISK32 and FORMAT32 allow one to prepare FAT32 disks. Additional utilities are taken from PC DOS 2000, where needed. In 1986, IBM announced PC DOS support for client access to

2450-534: The OS's release. In any case, IBM's original plans for the AT had been to equip it with a proper next-generation OS that would use its extended features, but this never materialized. PC DOS 3.1 (released March 1985) fixed the bugs in DOS 3.00 and supported IBM's Network Adapter card on the IBM PC Network . PC DOS 3.2 added support for 3 + 1 ⁄ 2 -inch double-density 720 KB floppy disk drives, supporting

2520-533: The PC 32 series were available with FlexOS as well. The Japanese post office shared terminals CTM  [ ja ] III and CTM IV were based on FlexOS. Computer multitasking Multitasking does not require parallel execution of multiple tasks at exactly the same time; instead, it allows more than one task to advance over a given period of time. Even on multiprocessor computers, multitasking allows many more tasks to be run than there are CPUs. Multitasking

2590-467: The agreement. At the same time, IBM released its next generation of personal computers, the IBM Personal System/2 (PS/2). PC DOS 3.3, released with the PS/2 line, added support for high density 3 + 1 ⁄ 2 -inch 1.44 MB floppy disk drives, which IBM introduced in its 80286-based and higher PS/2 models. The upgrade from DOS 3.2 to 3.3 was completely written by IBM, with no development effort on

2660-650: The basis of their IBM 4680 computer for IBM Plant System products and Point-of-Sale terminals in 1986. The last release of the IBM 4680 OS has been Version 4, before it was replaced by IBM 4690 Version 1. Versions: 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

2730-480: The companies made minor modifications to their version of DOS. In the fall of 1984, IBM gave all the source code and documentation of the internally developed IBM TopView for DOS to Microsoft so that Microsoft could more fully understand how to develop an object-oriented operating environment , overlapping windows (for its development of Windows 2.0 ) and multitasking . Microsoft first licensed, then purchased 86-DOS from Seattle Computer Products (SCP), which

2800-496: The context of this program was stored away, and the second program in memory was given a chance to run. The process continued until all programs finished running. The use of multiprogramming was enhanced by the arrival of virtual memory and virtual machine technology, which enabled individual programs to make use of memory and operating system resources as if other concurrently running programs were, for all practical purposes, nonexistent. Multiprogramming gives no guarantee that

2870-433: The early days of computing, CPU time was expensive, and peripherals were very slow. When the computer ran a program that needed access to a peripheral, the central processing unit (CPU) would have to stop executing program instructions while the peripheral processed the data. This was usually very inefficient. Multiprogramming is a computing technique that enables multiple programs to be concurrently loaded and executed into

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2940-489: The entire environment unacceptably fragile. Preemptive multitasking allows the computer system to more reliably guarantee to each process a regular "slice" of operating time. It also allows the system to deal rapidly with important external events like incoming data, which might require the immediate attention of one or another process. Operating systems were developed to take advantage of these hardware capabilities and run multiple processes preemptively. Preemptive multitasking

3010-484: The idea that the most efficient way for cooperating processes to exchange data would be to share their entire memory space. Thus, threads are effectively processes that run in the same memory context and share other resources with their parent processes , such as open files. Threads are described as lightweight processes because switching between threads does not involve changing the memory context. While threads are scheduled preemptively, some operating systems provide

3080-613: The new features from MS-DOS 6.0 appeared in PC ;DOS 6.1 including the new boot menu support and the new commands CHOICE , DELTREE , and MOVE . QBasic was dropped and the MS-DOS Editor was replaced with the IBM E Editor . It also licensed components of Central Point's PC Tools , such as Central Point Backup Utility (CPBACKUP). PC DOS 6.1 reports itself as DOS 6.00. PC DOS 6.3 followed in December. PC DOS 6.3

3150-509: The number of people he had to deal with at the ESD (Entry Systems Division) facility in Boca Raton, Florida . Perhaps the first public mention of the operating system was in July 1981, when Byte discussed rumors of a forthcoming personal computer with "a CP/M-like DOS ... to be called, simply, 'IBM Personal Computer DOS ' ". 86-DOS was rebranded IBM PC DOS 1.0 for its August 1981 release with

3220-480: The only disk format supported. In late 1981, Paterson, now at Microsoft, began writing PC DOS 1.10. It debuted in May 1982 along with the Revision ;B IBM PC. Support for the new double-sided drives was added, allowing 320 KB per disk. A number of bugs were fixed, and error messages and prompts were made less cryptic. The DEBUG.EXE was now able to load files greater than 64 KB in size. Later,

3290-468: The operating system kernel, in combination with hardware mechanisms that provide supporting functionalities, such as a memory management unit (MMU). If a process attempts to access a memory location outside its memory space, the MMU denies the request and signals the kernel to take appropriate actions; this usually results in forcibly terminating the offending process. Depending on the software and kernel design and

3360-554: The original Concurrent DOS system architecture found a continuation in successors like Concurrent DOS XM and Concurrent DOS 386 as well. Concurrent DOS 286, Concurrent DOS 68K and FlexOS were designed by Francis "Frank" R. Holsworth (using siglum FRH). Like Portable CP/M , Concurrent DOS 286 , Concurrent DOS 68K and Concurrent DOS V60 , FlexOS was written in C for higher portability across hardware platforms, and it featured very low interrupt latency and fast context switching. The original protected mode FlexOS 286 version 1.3

3430-486: The overall program. A processor intended for use with multitasking operating systems may include special hardware to securely support multiple tasks, such as memory protection , and protection rings that ensure the supervisory software cannot be damaged or subverted by user-mode program errors. The term "multitasking" has become an international term, as the same word is used in many other languages such as German, Italian, Dutch, Romanian, Czech, Danish and Norwegian. In

3500-540: The part of Microsoft, who were working on "Advanced DOS 1.0". DOS 3.30 was the last version designed with the IBM XT and floppy-only systems in mind; it became one of the most popular versions and many users preferred it to its buggy successor. PC DOS 4.0 (internally known as DOS 3.4 originally) shipped July 1988. DOS 4.0 had some compatibility issues with low-level disk utilities due to some internal data structure changes. DOS 4.0 used more memory than DOS 3.30 and it also had

3570-668: 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 (see LOADALL ). These problems had already caused delays in the delivery of Concurrent DOS 286 earlier. 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). FlexOS 386 provided

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3640-518: The running process hits a point where it has to wait for some portion of memory to be reloaded from secondary storage. Processes that are entirely independent are not much trouble to program in a multitasking environment. Most of the complexity in multitasking systems comes from the need to share computer resources between tasks and to synchronize the operation of co-operating tasks. Various concurrent computing techniques are used to avoid potential problems caused by multiple tasks attempting to access

3710-539: The same resource. Bigger systems were sometimes built with a central processor(s) and some number of I/O processors , a kind of asymmetric multiprocessing . Over the years, multitasking systems have been refined. Modern operating systems generally include detailed mechanisms for prioritizing processes, while symmetric multiprocessing has introduced new complexities and capabilities. PC DOS 3.2 IBM PC DOS (an acronym for IBM Personal Computer Disk Operating System ), also known as PC DOS or IBM DOS ,

3780-801: The specific error in question, the user may receive an access violation error message such as "segmentation fault". In a well designed and correctly implemented multitasking system, a given process can never directly access memory that belongs to another process. An exception to this rule is in the case of shared memory; for example, in the System V inter-process communication mechanism the kernel allocates memory to be mutually shared by multiple processes. Such features are often used by database management software such as PostgreSQL. Inadequate memory protection mechanisms, either due to flaws in their design or poor implementations, allow for security vulnerabilities that may be potentially exploited by malicious software. Use of

3850-509: The use of the High Memory Area (HMA) and Upper Memory Blocks (UMBs) on 80286 and later systems to reduce its conventional memory usage. Also all DOS commands now supported the /? option to display command syntax. Aside from IBM's PC DOS, MS-DOS was the only other version available as OEM editions vanished since by this time PCs were 100% compatible so customizations for hardware differences were no longer necessary. The POWER.EXE

3920-478: 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. To support Java , IBM 4690 OS Version 2 added support for long filenames by means of a virtual filesystem (VFS) architecture and it introduced FAT32 volumes. According to "The Year of the Store?", IHL Consulting Group/RIS News, IBM 4690 OS still had

3990-406: Was DOS , which is also the generic term for disk operating system, and is shared with dozens of disk operating systems called DOS . The IBM task force assembled to develop the IBM PC decided that critical components of the machine, including the operating system, would come from outside vendors. This radical break from company tradition of in-house development was one of the key decisions that made

4060-552: Was also used in OS/2 for the PowerPC . PC DOS 6.3 also featured SuperStor disk compression technology from Addstor . PC DOS 7 was released in April 1995 and was the last release of DOS before IBM software development (other than the development IBM ViaVoice ) moved to Austin. The REXX programming language was added, as well as support for a new floppy disk format, XDF , which extended

4130-475: Was bought by their competitor Wind River Systems in February 2000. The following list of commands is supported by FlexOS: Known FlexOS versions include: Motorola 68000 / Freescale / NXP ColdFire MCF5251 platform: Intel 80286 platform: Intel 80186 / NEC V20 / V30 platform: Intel 80386 platform: NEC V60 platform: Named IBM 4680 OS Version 1, IBM originally chose DR Concurrent DOS 286 as

4200-451: Was completed, IBM had a team of developers covering the full OS. At that point in time, either IBM or Microsoft completely developed versions of IBM PC DOS going forward. By 1985, the joint development agreement (JDA) between IBM and Microsoft for the development of PC DOS had each company giving the other company a completely developed version. Most of the time branded versions were identical, but there were some cases in which each of

4270-405: Was dedicated to their use, while behind the scenes the computer is serving many users by multitasking their individual programs. In multiprogramming systems, a task runs until it must wait for an external event or until the operating system's scheduler forcibly swaps the running task out of the CPU. Real-time systems such as those designed to control industrial robots, require timely processing;

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4340-409: Was designed for host machines equipped with 286 CPUs, and with adaptations for NEC V60 , NEC V70 and Motorola 68000 processors planned. FlexOS 286 executables using the system's native INT DCh ( INT 220 ) application program interface had the filename extension .286 . A CP/M API front-end (FE) was available as well, using the extension .CMD for executables. (A filename extension of .68K

4410-469: Was eventually supported by many computer operating systems , is known today as cooperative multitasking. Although it is now rarely used in larger systems except for specific applications such as CICS or the JES2 subsystem, cooperative multitasking was once the only scheduling scheme employed by Microsoft Windows and classic Mac OS to enable multiple applications to run simultaneously. Cooperative multitasking

4480-680: Was implemented in the PDP-6 Monitor and Multics in 1964, in OS/360 MFT in 1967, and in Unix in 1969, and was available in some operating systems for computers as small as DEC's PDP-8; it is a core feature of all Unix-like operating systems, such as Linux , Solaris and BSD with its derivatives , as well as modern versions of Windows. At any specific time, processes can be grouped into two categories: those that are waiting for input or output (called " I/O bound "), and those that are fully utilizing

4550-725: Was in the design of real-time computing systems, where there are a number of possibly unrelated external activities needed to be controlled by a single processor system. In such systems a hierarchical interrupt system is coupled with process prioritization to ensure that key activities were given a greater share of available process time . As multitasking greatly improved the throughput of computers, programmers started to implement applications as sets of cooperating processes (e. g., one process gathering input data, one process processing input data, one process writing out results on disk). This, however, required some tools to allow processes to efficiently exchange data. Threads were born from

4620-488: Was introduced that has the APM standard in version 5.02. This was the last version of DOS that IBM and Microsoft shared the full code for, and the DOS that was integrated into OS/2 2.0's, and later Windows NT's, virtual DOS machine . PC DOS remained a rebranded version of MS-DOS until 1993. IBM and Microsoft parted ways—MS-DOS 6 was released in March, and PC DOS 6.1 (separately developed) followed in June. Most of

4690-507: Was modified for the IBM PC by Microsoft employee Bob O'Rear with assistance from SCP (later Microsoft) employee Tim Paterson . O'Rear got 86-DOS to run on the prototype PC in February 1981. 86-DOS had to be converted from 8-inch to 5.25-inch floppy disks and integrated with the BIOS , which Microsoft was helping IBM to write. IBM had more people writing requirements for the computer than Microsoft had writing code. O'Rear often felt overwhelmed by

4760-560: Was released. In October 1983 (officially 1 November 1983) DOS 2.1 debuted. It fixed some bugs and added support for half-height floppy drives and the new IBM PCjr . In 1983, Compaq released the Compaq Portable , the first 100% IBM PC compatible and licensed their own OEM version of DOS 1.10 (quickly replaced by DOS 2.00) from Microsoft. Other PC compatibles followed suit, most of which included hardware-specific DOS features, although some were generic. In August 1984, IBM introduced

4830-580: Was reserved for FlexOS 68K, a file extension derived from Concurrent DOS 68K as of 1986.) 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,

4900-502: Was used as the primary test platform for the new Novell Embedded Systems Technology (NEST). 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 million in July 1994. The deal comprised

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