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86-431: Multiuser DOS is a real-time multi-user multi-tasking operating system for IBM PC -compatible microcomputers. An evolution of the older Concurrent CP/M-86 , Concurrent DOS and Concurrent DOS 386 operating systems, it was originally developed by Digital Research and acquired and further developed by Novell in 1991. Its ancestry lies in the earlier Digital Research 8-bit operating systems CP/M and MP/M , and

172-419: A deadlock , two or more tasks lock mutex without timeouts and then wait forever for the other task's mutex, creating a cyclic dependency. The simplest deadlock scenario occurs when two tasks alternately lock two mutex, but in the opposite order. Deadlock is prevented by careful design. The other approach to resource sharing is for tasks to send messages in an organized message passing scheme. In this paradigm,

258-559: 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

344-420: A complete PC, this offered considerable cost savings, as well as facilitating multi-user applications such as accounts or stock control in a time when PC networks were rare, very expensive and difficult to implement. CP/M-86 1.1 (with BDOS 2.2) and MP/M-86 2.1 were merged to create Concurrent CP/M-86 3.0 (also known as CCP/M-86) with BDOS 3.0 in late 1982. Kathryn Strutynski , the project manager for CP/M-86,

430-514: 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

516-415: A few tasks but occasionally contains more, then the list should be sorted by priority, so that finding the highest priority task to run does not require traversing the list. Instead, inserting a task requires walking the list. During this search, preemption should not be inhibited. Long critical sections should be divided into smaller pieces. If an interrupt occurs that makes a high priority task ready during

602-468: A flag or sending a message. A scheduler often provides the ability to unblock a task from interrupt handler context. An OS maintains catalogues of objects it manages such as threads, mutexes, memory, and so on. Updates to this catalogue must be strictly controlled. For this reason, it can be problematic when an interrupt handler calls an OS function while the application is in the act of also doing so. The OS function called from an interrupt handler could find

688-630: 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

774-449: A late answer is a wrong answer in a hard RTOS while a late answer is acceptable in a soft RTOS. The chief design goal is not high throughput , but rather a guarantee of a soft or hard performance category. An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS. An RTOS has an advanced algorithm for scheduling . Scheduler flexibility enables

860-506: A license to further develop Multiuser DOS from Novell in 1994 and renamed their product REAL/32 in 1995. Similar to FlexOS / 4690 OS before, IBM in 1995 licensed REAL/32 7.50 to bundle it with their 4695 POS terminals. IMS REAL/32 versions: REAL/32 7.50 to 7.74 report themselves as "IBM PC DOS" version 3.31, whereas 7.80 and higher report a version of 6.20. LBA and FAT32 support was added with REAL/32 7.90 in 1999. On 19 April 2002, Intelligent Micro Software Ltd. filed for insolvency and

946-417: A minimum, interrupt handlers are typically kept as short as possible. The interrupt handler defers all interaction with the hardware if possible; typically all that is necessary is to acknowledge or disable the interrupt (so that it won't occur again when the interrupt handler returns) and notify a task that work needs to be done. This can be done by unblocking a driver task through releasing a semaphore, setting

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1032-486: A multi-user operating system its price was higher than a single-user system, of course, and it required special device drivers, unlike single-user multitasking DOS add-ons such as Quarterdeck's DESQview . Unlike MP/M, it never became popular for single-user but multitasking use. When Novell acquired Digital Research in 1991 and abandoned Multiuser DOS in 1992, the three Master VARs DataPac Australasia, Concurrent Controls and Intelligent Micro Software were allowed to license

1118-517: A mutex, but the lower priority task is not given CPU time to finish its work. A typical solution is to have the task that owns a mutex 'inherit' the priority of the highest waiting task. But this simple approach gets more complex when there are multiple levels of waiting: task A waits for a mutex locked by task B , which waits for a mutex locked by task C . Handling multiple levels of inheritance causes other code to run in high priority context and thus can cause starvation of medium-priority threads. In

1204-427: A network server . Concurrent DOS 386 allowed a single server to support a number of users on dumb terminals or inexpensive low-specification PCs running terminal emulation software, without the need for expensive workstations and then-expensive network cards. It was a true multiuser system; several users could use a single database with record locking to prevent mutual interference. Concurrent DOS 6.0 represented also

1290-558: A reengineered derivation of Concurrent DOS 286, which was developed by Digital Research's new Flexible Automation Business Unit in Monterey, California, since 1986. Later versions added compatibility with PC DOS 2.x and 3.x. Known versions include: The OEM Support Group was relocated into Digital Research's newly created European Development Centre (EDC) in Hungerford , UK in 1986, which started to take over further development of

1376-476: 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

1462-411: A successor to CP/M-68K written in C . One of its main architects was Francis "Frank" R. Holsworth (using siglum FRH). Concurrent DOS 68K 1.0 became available for OEM evaluation in early 1985. The effort received considerable funding worth several million dollars from Motorola and was designed for their 68000 / 68010 processors. Like the earlier GEMDOS system for 68000 processors it initially ran on

1548-428: A task is working on a low-priority message and ignores a higher-priority message (or a message originating indirectly from a high priority task) in its incoming message queue. Protocol deadlocks can occur when two or more tasks wait for each other to send response messages. Since an interrupt handler blocks the highest priority task from running, and since real-time operating systems are designed to keep thread latency to

1634-428: 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 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

1720-405: A wider, computer-system orchestration of process priorities, but a real-time OS is more frequently dedicated to a narrow set of applications. Key factors in a real-time OS are minimal interrupt latency and minimal thread switching latency ; a real-time OS is valued more for how quickly or how predictably it can respond than for the amount of work it can perform in a given period of time. An RTOS

1806-428: Is an operating system in which the time taken to process an input stimulus is less than the time lapsed until the next input stimulus of the same type. The most common designs are: Time sharing designs switch tasks more often than strictly needed, but give smoother multitasking , giving the illusion that a process or user has sole use of a machine. Early CPU designs needed many cycles to switch tasks during which

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1892-449: Is better to use mechanisms also available on general-purpose operating systems, such as a mutex and OS-supervised interprocess messaging. Such mechanisms involve system calls, and usually invoke the OS's dispatcher code on exit, so they typically take hundreds of CPU instructions to execute, while masking interrupts may take as few as one instruction on some processors. A (non-recursive) mutex

1978-403: Is either locked or unlocked. When a task has locked the mutex, all other tasks must wait for the mutex to be unlocked by its owner - the original thread. A task may set a timeout on its wait for a mutex. There are several well-known problems with mutex based designs such as priority inversion and deadlocks . In priority inversion a high priority task waits because a low priority task has

2064-409: Is enough free memory. Secondly, speed of allocation is important. A standard memory allocation scheme scans a linked list of indeterminate length to find a suitable free memory block, which is unacceptable in a RTOS since memory allocation has to occur within a certain amount of time. Because mechanical disks have much longer and more unpredictable response times, swapping to disk files is not used for

2150-467: Is frowned upon. Whenever possible, all required memory allocation is specified statically at compile time. Another reason to avoid dynamic memory allocation is memory fragmentation. With frequent allocation and releasing of small chunks of memory, a situation may occur where available memory is divided into several sections and the RTOS cannot allocate a large enough continuous block of memory, although there

2236-525: Is the lowest overhead method to prevent simultaneous access to a shared resource. While interrupts are masked and the current task does not make a blocking OS call, the current task has exclusive use of the CPU since no other task or interrupt can take control, so the critical section is protected. When the task exits its critical section, it must unmask interrupts; pending interrupts, if any, will then execute. Temporarily masking interrupts should only be done when

2322-485: The 16-bit single-tasking CP/M-86 which evolved from CP/M. When Novell abandoned Multiuser DOS in 1992, the three master value-added resellers (VARs) DataPac Australasia, Concurrent Controls and Intelligent Micro Software were allowed to take over and continued independent development into Datapac Multiuser DOS and System Manager, CCI Multiuser DOS, and IMS Multiuser DOS and REAL/32. The FlexOS line, which evolved from Concurrent DOS 286 and Concurrent DOS 68K ,

2408-567: 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

2494-554: 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

2580-655: The Internet Archive , seems to be the latest release. By 2005, the realng.com website was mirroring the IMS main website, and had no mention of REAL/NG, only REAL/32. While the various releases of this operating system had increasing ability to run DOS programs, software written for the platform could take advantage of its features by using function calls specifically suitable for multiuser operation. It used pre-emptive multitasking , preventing badly-written applications from delaying other processes by retaining control of

2666-526: The System Management Mode on x86 compatible hardware can take a lot of time before it returns control to the operating system. Memory allocation is more critical in a real-time operating system than in other operating systems. First, for stability there cannot be memory leaks (memory that is allocated but not freed after use). The device should work indefinitely, without ever needing a reboot. For this reason, dynamic memory allocation

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2752-608: The WordStar word processor for DOS, would not, and native Concurrent CP/M (or CP/M-86) versions were required. While Concurrent DOS 3.1 up to 4.1 had been developed in the US, OEM adaptations and localizations were carried out by DR Europe 's OEM Support Group in Newbury , UK, since 1983. Digital Research positioned Concurrent DOS 4.1 with GEM as alternative for IBM 's TopView in 1985. Concurrent DOS 3.2 (with BDOS 3.2) in 1984

2838-411: 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

2924-435: 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 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

3010-523: The 8-bit or the 16-bit processor, depending on whether the executable file had a .COM or .CMD extension. It emulated a CP/M environment for 8-bit programs by translating CP/M system calls into CP/M-86 system calls, which were then executed by the 16-bit processor. In August 1983, Bruce Skidmore, Raymond D. Pedrizetti, Dave Brown and Gordon Edmonds teamed up to create PC-MODE, an optional module for Concurrent CP/M-86 3.1 (with BDOS 3.1) to provide basic compatibility with PC DOS 1.1 (and MS-DOS 1.1 ). This

3096-411: The CPU could do nothing else useful. Because switching took so long, early OSes tried to minimize wasting CPU time by avoiding unnecessary task switching. In typical designs, a task has three states: Most tasks are blocked or ready most of the time because generally only one task can run at a time per CPU core . The number of items in the ready queue can vary greatly, depending on the number of tasks

3182-588: The Concurrent DOS family since Concurrent DOS 4.11, including siblings like DOS Plus and successors. Developed in Hungerford, UK, versions 5 and 6 (Concurrent DOS XM, with XM standing for Expanded Memory ) could bank switch up to 8 MB of EEMS to provide a real-mode environment to run multiple CP/M-86 and DOS programs concurrently and support up to three users (one local and up to two hooked up via serial terminals). In 1987, Concurrent DOS 86

3268-477: 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 )

3354-671: 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 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

3440-523: 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

3526-721: 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

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3612-491: The LSI-M4, LSI Octopus and CAL PC computers. These machines had both 16-bit and 8-bit processors, because in the early days of 16-bit personal computing, 8-bit software was more available and often ran faster than the corresponding 16-bit software. Concurrent CP/M-86/80 allowed users to run both CP/M (8-bit) and CP/M-86 (16-bit) applications. When a command was entered, the operating system ran the corresponding application on either

3698-664: The Motorola VME /10 development system. Concurrent DOS 68K 1.20/1.21 was available in April 1986, offered for about 200 000  dollars to OEMs. This system evolved into FlexOS 68K in late 1986. Known versions include: In parallel to the Concurrent DOS 68K effort, Digital Research also previewed Concurrent DOS 286 in cooperation with Intel in January 1985. This was based on MP/M-286 and Concurrent CP/M-286, on which Digital Research had worked since 1982. Concurrent DOS 286

3784-400: The OS related work to a separate handler. This handler runs at a higher priority than any thread but lower than the interrupt handlers. The advantage of this architecture is that it adds very few cycles to interrupt latency. As a result, OSes which implement the segmented architecture are more predictable and can deal with higher interrupt rates compared to the unified architecture. Similarly,

3870-496: 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

3956-575: The PC-compatible world, such as graphics adaptors , sound cards , CD-ROM drives and mice. Although many of these were soon rectified – for example, graphical terminals were developed, allowing users to use CGA , EGA and VGA software – it was less flexible in this regard than a network of individual PCs, and as the prices of these fell, it became less and less competitive, although it still offered benefits in terms of management and lower total cost of ownership. As

4042-792: The Sydney-based unit was spun out into Citrix' Advanced Products Group. Known CCI Multiuser DOS versions by Concurrent Controls, Inc. (CCI) include: All versions of CCI Multiuser DOS report themselves as "IBM PC DOS" version 3.31. Similar to SETVER under DOS , this can be changed using the Multiuser DOS DOSVER ;x.y utility. In 1999, CCI changed its name to Applica, Inc. In 2002 Applica Technology became Aplycon Technologies, Inc. Known adaptations of IMS Multiuser DOS include: All versions of IMS Multiuser DOS report themselves as "IBM PC DOS" version 3.31. Intelligent Micro Software Ltd. (IMS) of Thatcham , UK, acquired

4128-471: 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

4214-678: 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 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

4300-551: The emulation on the production level C-1 step of the processor in May, which would not allow Concurrent DOS 286 to run 8086 software in protected mode. The release of Concurrent DOS 286 had been scheduled for late May, but was delayed until Intel could develop a new version of the chip. In August, after extensive testing E-1 step samples of the 80286, Digital Research said that Intel had corrected all documented 286 errata , but that there were still undocumented chip performance problems with

4386-503: The enhanced functionality of DR's later single-user PC DOS clone DR DOS 5.0 , after which the product was given the more explanatory name "Multiuser DOS" (a.k.a. MDOS), starting with version 5.0 (with BDOS 6.5) in 1991. Multiuser DOS suffered from several technical limitations that restricted its ability to compete with LANs based on PC DOS . It required its own special device drivers for much common hardware, as PC DOS drivers were not multiuser or multi-tasking aware. Driver installation

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4472-527: The highest priority to jobs with the lowest demand on the computer, so there is no way to ensure that a time-critical job will have access to enough resources. Multitasking systems must manage sharing data and hardware resources among multiple tasks. It is usually unsafe for two tasks to access the same specific data or hardware resource simultaneously. There are three common approaches to resolve this problem: General-purpose operating systems usually do not allow user programs to mask (disable) interrupts , because

4558-441: The highest-priority ready task will take 5 to 30 instructions. In advanced systems, real-time tasks share computing resources with many non-real-time tasks, and the ready list can be arbitrarily long. In such systems, a scheduler ready list implemented as a linked list would be inadequate. Some commonly used RTOS scheduling algorithms are: A multitasking operating system like Unix is poor at real-time tasks. The scheduler gives

4644-432: The insertion of a low priority task, that high priority task can be inserted and run immediately before the low priority task is inserted. The critical response time, sometimes called the flyback time, is the time it takes to queue a new ready task and restore the state of the highest priority task to running. In a well-designed RTOS, readying a new task will take 3 to 20 instructions per ready-queue entry, and restoration of

4730-514: The interactions of multiple programs. Later versions supported dumb terminals and so could be deployed as multiuser systems. Concurrent CP/M-86 3.1 (BDOS 3.1) shipped on 21 February 1984. In February 1984 Digital Research also offered a version of Concurrent CP/M-86 with windowing capabilities named Concurrent CP/M with Windows for the IBM Personal Computer and Personal Computer XT . This was an adaptation of Concurrent CP/M-86 for

4816-472: The longest path through the critical section is shorter than the desired maximum interrupt latency . Typically this method of protection is used only when the critical section is just a few instructions and contains no loops. This method is ideal for protecting hardware bit-mapped registers when the bits are controlled by different tasks. When the shared resource must be reserved without blocking all other tasks (such as waiting for Flash memory to be written), it

4902-679: 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

4988-569: 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

5074-496: The object database to be in an inconsistent state because of the application's update. There are two major approaches to deal with this problem: the unified architecture and the segmented architecture. RTOSs implementing the unified architecture solve the problem by simply disabling interrupts while the internal catalogue is updated. The downside of this is that interrupt latency increases, potentially losing interrupts. The segmented architecture does not make direct OS calls but delegates

5160-487: 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,

5246-544: 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

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5332-537: The prerelease version of Concurrent DOS 286 running on the E-1 step. Intel said that the approach Digital Research wished to take in emulating 8086 software in protected mode differed from the original specifications; nevertheless they incorporated into the E-2 step minor changes in the microcode that allowed Digital Research to run emulation mode much faster (see LOADALL ). These same limitations affected FlexOS 286 version 1.x,

5418-444: The processor. To this day, Multiuser DOS is supported by popular SSL/TLS libraries such as wolfSSL . Real-time operating system A key characteristic of an RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task ; the variability is " jitter ". A "hard" real-time operating system (hard RTOS) has less jitter than a "soft" real-time operating system (soft RTOS);

5504-528: 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, 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

5590-447: The resource is managed directly by only one task. When another task wants to interrogate or manipulate the resource, it sends a message to the managing task. Although their real-time behavior is less crisp than semaphore systems, simple message-based systems avoid most protocol deadlock hazards, and are generally better-behaved than semaphore systems. However, problems like those of semaphores are possible. Priority inversion can occur when

5676-504: The same reasons as RAM allocation discussed above. The simple fixed-size-blocks algorithm works quite well for simple embedded systems because of its low overhead. PC DOS 1.1 IBM PC DOS (an acronym for IBM Personal Computer Disk Operating System ), also known as PC DOS or IBM DOS , is a discontinued disk operating system for the IBM Personal Computer , its successors, and IBM PC compatibles . It

5762-419: The source code of the system to take over and continue independent development of their derivations in 1994. Known versions include: All versions of Digital Research and Novell DR Multiuser DOS reported themselves as "IBM PC DOS" version 3.31. Known versions by DataPac Australasia Pty Limited include: In 1997, Datapac was bought by Citrix Systems, Inc. , and System Manager was abandoned soon after. In 2002

5848-463: The starting point for the DR DOS family, which was carved out of it. Known versions include: Concurrent PC DOS XM 5.0 emulated IBM PC DOS 2.10, whereas Concurrent DOS XM 6.0 and Concurrent DOS 386 2.0 were compatible with IBM PC DOS 3.30. Known CCI Concurrent DOS adaptations by Concurrent Controls, Inc. include: Other adaptations include: Later versions of Concurrent DOS 386 incorporated some of

5934-413: The system needs to perform and the type of scheduler that the system uses. On simpler non-preemptive but still multitasking systems, a task has to give up its time on the CPU to other tasks, which can cause the ready queue to have a greater number of overall tasks in the ready to be executed state ( resource starvation ). Usually, the data structure of the ready list in the scheduler is designed to minimize

6020-517: 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

6106-547: The user program could control the CPU for as long as it is made to. Some modern CPUs do not allow user mode code to disable interrupts as such control is considered a key operating system resource. Many embedded systems and RTOSs, however, allow the application itself to run in kernel mode for greater system call efficiency and also to permit the application to have greater control of the operating environment without requiring OS intervention. On single-processor systems, an application running in kernel mode and masking interrupts

6192-431: The worst-case length of time spent in the scheduler's critical section, during which preemption is inhibited, and, in some cases, all interrupts are disabled, but the choice of data structure depends also on the maximum number of tasks that can be on the ready list. If there are never more than a few tasks on the ready list, then a doubly linked list of ready tasks is likely optimal. If the ready list usually contains only

6278-608: Was a complete rewrite in the C language based on a new system architecture with dynamically loadable device drivers instead of a static BIOS or XIOS. One of its main architects was Francis "Frank" R. Holsworth. The operating system would function strictly in 80286 native mode, allowing protected mode multi-user , multitasking operation while running 8086 emulation . While this worked on the B-1 step of prototype chip samples, Digital Research, with evaluation copies of their operating system already shipping in April, discovered problems with

6364-438: Was also the project manager for Concurrent CP/M-86. One of its designers was Francis "Frank" R. Holsworth. Initially, this was a single-user operating system supporting true multi-tasking of up to four (in its default configuration) CP/M-86 compatible programs. Like its predecessors it could be configured for multi-processor support (see e.g. Concurrent CP/M-86/80) and also added "virtual screens" letting an operator switch between

6450-513: 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

6536-476: Was compatible with applications for CP/M-86 1.x, Concurrent CP/M-86 3.x and PC DOS 2.0. It was available for many different hardware platforms. The version with an IBM PC compatible BIOS/XIOS was named Concurrent PC DOS 3.2. Kathryn Strutynski was the product manager for Concurrent PC DOS. Efforts being part of a cooperation with Motorola since 1984 led to the development of Concurrent DOS 68K in Austin , Texas, as

6622-491: 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

6708-490: 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 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

6794-567: 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

6880-526: Was more complex than the simple PC DOS method of copying the files onto the boot disk and modifying CONFIG.SYS appropriately – it was necessary to relink the Multiuser DOS kernel (known as a nucleus ) using the SYSGEN command. Multiuser DOS was also unable to use many common PC DOS additions such as network stacks , and it was limited in its ability to support later developments in

6966-567: 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

7052-485: Was rewritten to become Concurrent DOS 386, still a continuation of the classical XIOS & BDOS architecture. This ran on machines equipped with the Intel 80386 and later processors, using the 386's hardware facilities for virtualizing the hardware, allowing most DOS applications to run unmodified under Concurrent DOS 386, even on terminals. The OS supported concurrent multiuser file access, allowing multiuser applications to run as if they were on individual PCs attached to

7138-505: Was shown publicly at COMDEX in December 1983 and shipped in March 1984 as Concurrent DOS 3.1 (a.k.a. CDOS with BDOS 3.1) to hardware vendors. Simple DOS applications, which did not directly access the screen or other hardware, could be run. For example, although a console program such as PKZIP worked perfectly and offered more facilities than the CP/M-native ARC archiver, applications which performed screen manipulations, such as

7224-465: Was sold off to Integrated Systems , Inc. (ISI) in July 1994. The initial version of CP/M-86 1.0 (with BDOS 2.x) was adapted and became available to the IBM PC in 1982. It was commercially unsuccessful as IBM 's PC DOS 1.0 offered much the same facilities for a considerably lower price. Neither PC DOS nor CP/M-86 could fully exploit the power and capabilities of the new 16-bit machine. It

7310-427: Was soon supplemented by an implementation of CP/M's multitasking 'big brother', MP/M-86 2.0 , since September 1981. This turned a PC into a multiuser machine capable of supporting multiple concurrent users using dumb terminals attached by serial ports . The environment presented to each user made it seem as if they had the entire computer to themselves. Since terminals cost a fraction of the then-substantial price of

7396-592: Was taken over by one of its major customers, Barry Quittenton's Itera Ltd. This company was dissolved on 2006-03-28. As of 2010 REAL/32 was supplied by Integrated Solutions of Thatcham, UK, but the company, at the same address, was later listed as builders. REAL/NG was IMS' attempt to create the "Next Generation" of REAL/32, also named "REAL/32 for the internet age". REAL/NG promised "increased range of hardware from PCs to x86 multi-processor server systems". Advertised feature list, as of 2003: By 10 December 2003, IMS made "REALNG V1.60-V1.19-V1.12" available, which, based on

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