Multiuser DOS is a soft
real-timeA real-time operating system is a multitasking operating system intended for real-time applications. Such applications include embedded systems , industrial robots, spacecraft, industrial control , and scientific research equipment.A RTOS facilitates the creation of a real-time system, but does not...
operating systemAn operating system is an interface between hardware and user which is responsible for the management and coordination of activities and the sharing of the resources of the computer that acts as a host for computing applications run on the machine. As a host, one of the purposes of an operating...
for
IBM PCThe IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
-compatible microcomputers.
An evolution of the older
Concurrent CP/M and
Concurrent DOS operating systems, it was originally developed by
Digital ResearchDigital Research, Inc. was the company created by Dr. Gary Kildall to market and develop his CP/M operating system and related products. It was the first large software company in the microcomputer world. Digital Research should not be confused with Digital Equipment Corporation; the two were not...
. Its ancestry lies in the earlier DR operating systems
CP/MCP/M is an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
and
MP/MMP/M was the multi-user version of the CP/M operating system, created by Digital Research developer Tom Rolander in 1979. It allowed multiple users to connect to a single computer, each using a separate terminal....
.
The initial version of CP/M for the IBM PC,
CP/M-86, was commercially unsuccessful, as
MicrosoftMicrosoft Corporation is a multinational computer technology corporation that develops, manufactures, licenses, and supports a wide range of software products for computing devices...
's
MS-DOSMS-DOS is an operating system developed by Microsoft. It was the most commonly used member of the DOS family of operating systems and was the main operating system for personal computers during the 1980s. It was preceded by M-DOS , designed and copyrighted by Microsoft in 1979...
offered much the same facilities for a considerably lower price.
Multiuser DOS is a soft
real-timeA real-time operating system is a multitasking operating system intended for real-time applications. Such applications include embedded systems , industrial robots, spacecraft, industrial control , and scientific research equipment.A RTOS facilitates the creation of a real-time system, but does not...
operating systemAn operating system is an interface between hardware and user which is responsible for the management and coordination of activities and the sharing of the resources of the computer that acts as a host for computing applications run on the machine. As a host, one of the purposes of an operating...
for
IBM PCThe IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
-compatible microcomputers.
An evolution of the older
Concurrent CP/M and
Concurrent DOS operating systems, it was originally developed by
Digital ResearchDigital Research, Inc. was the company created by Dr. Gary Kildall to market and develop his CP/M operating system and related products. It was the first large software company in the microcomputer world. Digital Research should not be confused with Digital Equipment Corporation; the two were not...
. Its ancestry lies in the earlier DR operating systems
CP/MCP/M is an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
and
MP/MMP/M was the multi-user version of the CP/M operating system, created by Digital Research developer Tom Rolander in 1979. It allowed multiple users to connect to a single computer, each using a separate terminal....
.
The initial version of CP/M for the IBM PC,
CP/M-86, was commercially unsuccessful, as
MicrosoftMicrosoft Corporation is a multinational computer technology corporation that develops, manufactures, licenses, and supports a wide range of software products for computing devices...
's
MS-DOSMS-DOS is an operating system developed by Microsoft. It was the most commonly used member of the DOS family of operating systems and was the main operating system for personal computers during the 1980s. It was preceded by M-DOS , designed and copyrighted by Microsoft in 1979...
offered much the same facilities for a considerably lower price. Like MS-DOS 1.0, CP/M-86 did not fully exploit the power and capabilities of the new
16-bit-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor.Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816...
machine.
It was soon superseded by an implementation of CP/M's multitasking 'big brother',
MP/M-86. This turned a PC into a multiuser machine capable of supporting multiple concurrent users using dumb terminals attached by
serial portIn computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
s. 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 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 and MP/M-86 were later merged to create Concurrent CP/M (also known as
CCP/M), which offered more complete CP/M-86 compatibility in addition to MP/M-86's multiuser capabilities.
As the origin of MS-DOS was as a clone of CP/M, this operating system also offered limited compatibility with MS-DOS - simple MS-DOS applications which did not directly access the screen or other hardware could be run under CCP/M. For example, although a console program such as
PKZipPKZIP is an archiving tool originally written by Phil Katz and marketed by his company PKWARE, Inc. The common "PK" prefix used in both PKZIP and PKWARE stands for Phil Katz...
worked perfectly and offered more facilities than the CP/M-native
Arc archiver, more complex applications which performed screen manipulations, such as
WordStarWordStar was a word processor application, published by MicroPro International, originally written for the CP/M operating system but later ported to DOS, that enjoyed a dominant market share during the early to mid-1980s. Although Seymour I...
for DOS, would not and thus native CCP/M versions were required.
CCP/M was developed into Concurrent DOS (AKA
CDOS), which offered more complete DOS compatibility. The first released version, CDOS 3.2, was compatible with MS-DOS 1; later versions added compatibility with MS-DOS 2.x and 3.x. Versions 5 and 6 (
Concurrent DOS XM) could
bank switchBank switching was a technique common in 8-bit microcomputer systems, to increase the amount of addressable RAM and ROM without extending the address bus...
multiple programs using
EEMSIn computers compatible with the IBM Personal Computer, expanded memory is a system of bank switching introduced around 1984 that provided additional memory to MS DOS or PC DOS programs beyond the limit of conventional memory. Expanded memory uses parts of the remaining 384 KB, normally dedicated...
.
In 1987, CDOS was rewritten as Concurrent DOS/386. This ran on machines equipped with the Intel 80386 processor (and later processors), using the 386's
hardwareHardware is a general term for the physical artifacts of a technology. It may also mean the physical components of a computer system, in the form of computer hardware....
facilities for virtualizing the hardware, allowing most DOS applications to run unmodified under CDOS/386, even on terminals. The OS supported concurrent multiuser file access, allowing multiuser DOS applications to run as if they were on individual PCs attached to a network
serverA server is an application running on a computer that delivers a service. For example, a web server will deliver web pages when requested by a browser . The way a server and a client dialogs is called a protocol...
. Thus CDOS/386 was not only a cheaper alternative to individual PCs but allowed a single server to support a number of users on dumb terminals or low-specification PCs running terminal emulation software, without the expense of individual workstations and network cards. Appropriate software allowed several users to use a single database without mutual interference: it was a true multiuser system.
Later versions of CDOS incorporated some of the enhanced functionality of DR's later single-user MS-DOS clone
DR-DOSDR-DOS is a DOS-type operating system for IBM PC-compatible personal computers, originally developed by Gary Kildall's Digital Research and derived from CP/M-86.-Origins in CP/M:...
, after which the product was renamed to the more explanatory Multiuser DOS, often abbreviated to MUDOS or MDOS.
MDOS suffered from several technical limitations that restricted its ability to compete with
LANLän are the Swedish and lääni Finnish language terms, respectively, for the administrative divisions used in Sweden and Finland.They are also sometimes used in other countries, especially as a translation of the Russian word oblast...
s based on
MS-DOSMS-DOS is an operating system developed by Microsoft. It was the most commonly used member of the DOS family of operating systems and was the main operating system for personal computers during the 1980s. It was preceded by M-DOS , designed and copyrighted by Microsoft in 1979...
. It required its own special device drivers for much common hardware, as MS-DOS drivers were not multiuser or multi-tasking aware. Driver installation was more complex than the simple MS-DOS method of copying the files onto the boot disk and modifying CONFIG.SYS appropriately - it was necessary to relink the MDOS kernel (known as a
nucleus) using the SYSGEN command.
MDOS was also unable to use many common MS-DOS additions such as network stacks, and it was limited in its ability to support later developments in 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
CGAThe Color Graphics Adapter , originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card, and the first color computer display standard for the IBM PC....
,
EGAThe Enhanced Graphics Adapter is the IBM PC computer display standard specification located between CGA and VGA in terms of color and space resolution. Introduced in 1984 by IBM for its new PC-AT, EGA produces a display of 16 simultaneous colors from a palette of 64 at a resolution of up to...
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. Unlike MP/M, it never became popular as a single-user but multitasking OS, partly because of license costs and partly because of the requirement for special device drivers—unlike multitasking, but single user, DOS additions such as Quarterdeck's
DESQviewDESQview was a text mode multitasking program developed by Quarterdeck Office Systems which enjoyed modest popularity in the late 1980s and early 1990s...
.
Applications software
While the various releases of this operating system had increasing ability to run MS-DOS programs, software written for the platform could take advantage of its features by using function calls specifically suitable for multiuser operation. The operating system provided pre-emptive multitasking so that no process could hog the processor and refuse to relinquish control; this was a problem with early software for
Microsoft WindowsMicrosoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces...
. There were facilities for processes to run in the background without user interaction, and for
communication between running processesInter-process communication is a set of techniques for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC techniques are divided into methods for message passing, synchronization, shared memory, and...
. Programs written, or adapted, for the platform (or any multitasking platform) needed to avoid the technique used by single-tasking systems of going into endless loops until interrupted when, for example, waiting for a user to press a key; this wasted processor time that could be used by other users. Instead, waiting programs could go into a sleep mode supported by the operating system which did not use resources. Processes could be run at different
priority levelPriority level or priority, in the Telecommunications Service Priority system, is the level that may be assigned to an NS/EP telecommunications service, which level specifies the order in which provisioning or restoration of the service is to occur relative to other NS/EP or non-NS/EP...
s.
See also
- CP/M
CP/M is an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
- DR-DOS
DR-DOS is a DOS-type operating system for IBM PC-compatible personal computers, originally developed by Gary Kildall's Digital Research and derived from CP/M-86.-Origins in CP/M:...
- FreeDOS
FreeDOS is an operating system for IBM PC compatible computers. FreeDOS is made up of many different, separate programs that act as "packages" to the overall FreeDOS Project...
- MP/M
MP/M was the multi-user version of the CP/M operating system, created by Digital Research developer Tom Rolander in 1979. It allowed multiple users to connect to a single computer, each using a separate terminal....
- OpenDOS
- PC-DOS
IBM PC DOS is a Proprietary DOS system for the IBM Personal Computer and compatibles, manufactured and sold by IBM from the 1980s to the 2000s.-Naming:Official product name of "PC DOS" are as below:...
- PC-MOS/386
PC-MOS/386 was a multi-user, multi-tasking operating system produced by The Software Link. It will run much MS-DOS software on the host machine or a terminal connected to it. Unlike MS-DOS, PC-MOS/386 is optimized for the Intel 80386 processor; however early versions will run on any x86...
- TSR
Terminate and Stay Resident is a computer system call in DOS computer operating systems that returns control to the system as if the program has quit, but keeps the program in memory...
, a method of conventional DOS for pseudo multitasking
External links