M-DOS
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Multiuser DOS
Multiuser DOS is a soft real-time multi-user multi-tasking operating system for IBM PC-compatible microcomputers.An evolution of the older Concurrent CP/M-86 and Concurrent DOS operating systems, it was originally developed by Digital Research and later further developed by Novell...

 by Digital Research
Digital Research
Digital 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...

 or Siemens
Siemens
Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...

 multi-tasking DOS
New Executable
The New Executable is a 16-bit .exe file format, a successor to the DOS MZ executable format. It was used in a special version of MS-DOS, Windows 1.0, Windows 2.x, and Windows 3.x...

 (nicknamed "European MS DOS 4.0").


M-DOS or MIDAS (as Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 called it from 1980 onwards) refers to an operating system that was designed by Marc McDonald of Microsoft in 1979. It was designed for the 8080/Z80 microprocessors, popular due to CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...

 at the time.

The Microsoft Disk Operating System
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 was designed to use terminal input/output and offered the following features:
  • Terminal interrupts for input and output
  • Ability to turn output terminal interrupts on and off without sending garbage characters
  • Clock interrupts used for MDOS scheduling and time accounting
  • Disk interrupts taking advantage of multiple sector I/O
  • 8-bit File Allocation Table
    File Allocation Table
    File Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...


Commands

MDOS was designed as a single user version as well as a multi-user
Multi-user
Multi-user is a term that defines an operating system or application software that allows concurrent access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving the...

 version (using relocation hardware). It was modelled closely on TOPS-10
TOPS-10
The TOPS-10 System was a computer operating system from Digital Equipment Corporation for the PDP-10 mainframe computer launched in 1967...

 on the DEC System-10. As such it was designed to offer the following commands:
  • Continue : Continue execution until CTL-C or exit.
  • DELete : Delete file
  • Deposit : Deposit value into location
  • EArom : Modify EAROM parameters
  • Examine : Examine location
  • DIrect : List file directory
  • Load : Load program into memory
  • Mount : Mount diskette
  • REMove : Remove diskette
  • REName : Rename file
  • Run : Run file
  • Save : Save user program
  • TErm : List/change terminal characteristics
  • Type : List file on terminal


It also included the following new commands
Command (computing)
In computing, a command is a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Most commonly a command is a directive to some kind of command line interface, such as a shell....

 (which at the time of design had no abbreviations):
  • MEMORY : List amount of memory being used
  • HEX : Make typein/type-out in Hex
  • OCTAL : Make type-in/typeout in octal
  • ASSIGN : Assign device to user
  • DEASSIGN : De assign device from user
  • RESOURCE : List available resources
  • MAP : List users and locations
  • PERFORM : List MDOS performance data

Design

MDOS included many systems calls (more than 65). Its interrupt driven design enabled the system software
System software
System software is computer software designed to operate the computer hardware and to provide a platform for running application software.The most basic types of system software are:...

 to use idle I/O time (when slow devices are being accessed) to do other tasks. It was designed to use structures (similar to structures in the C language) to keep tabs on every user and every task. Thus a high priority operation could stop a user task and restart it without losing anything. MDOS was designed to occupy only 9 kilobytes for its code and 2-3 kilobytes for its data. Multi-user
Multi-user
Multi-user is a term that defines an operating system or application software that allows concurrent access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving the...

 installations would need additional 50 bytes/user and 550-600 bytes per terminal. Upgrading the single user version to the multi-user would be no different to a program.

MDOS was designed to run on any 8080 or Z80 processor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

 (and even support the 8086 and the Z8000 processors at a later stage). It used data blocks such as a File Data Block (FDB) handling device independent I/O, a Unit Data Block (UDB) for physical disk I/O, a Structure Data Block (SDB) for logical data I/O and a Line Data Block (LDB) for Terminal I/O.

Every job contained a Job Data Area in the first 400 (Octal) memory locations (similar to MS-DOS). The user program starts at 400 (octal) and runs till the top of user memory (called .JBLOW)

MDOS also introduced the idea of memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....

 garbage collection
Garbage collection (computer science)
In computer science, garbage collection is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage, or memory occupied by objects that are no longer in use by the program...

 (implemented in Unix systems) for personal computers. Pointers to the free areas were arranged so that areas closer to the base of the area would be used first, and areas within larger free areas would be deleted and the larger area adjusted accordingly. Garbage collection would take place in single user mode, as free memory would be accessed.

Although MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...

 has a command structure where the new (file name, action etc.) precedes the old, MDOS followed the CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...

 notation
Notation
-Written communication:* Phonographic writing systems, by definition, use symbols to represent components of auditory language, i.e. speech, which in turn refers to things or ideas. The two main kinds of phonographic notational system are the alphabet and syllabary...

 where old precedes the new. For example the copy command would be:
  • COPY =


instead of the MS-DOS
  • COPY


MS-DOS was designed for the new 8086 series of computers and was launched with the IBM PC. (Although MS DOS could handle terminal I/O it was primarily used with integrated video boards.) This was a business deal that basically launched the commercial side of Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

and turned it into a multi-billion dollar company. Microsoft abandoned MDOS.
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