Multiprogramming
Encyclopedia
Computer multiprogramming is the allocation of a computer system and its resources to more than one concurrent application, job or user ("program" in this nomenclature).
Initially, this technology was sought in order to optimize use of a computer system, since time and processing resources were often wasted when a single job waited for human interaction was developed as a feature of operating systems in the late 1950s and came into common use in mainframe computing in the mid- to late 1960s. This followed the development of hardware systems that possessed the requisite circuit logic and instruction sets to facilitate the transfer of control between the operating system and one or more independent applications, users or job stream
s.
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, non-existent and invisible to them.
Multiprogramming should be differentiated from multi-tasking since not all multiprogramming entails—or has the capability for-- "true" multi-tasking. This is the case even though the use of multi-tasking generally implies the use of some multiprogramming methods.
In this context, the root word "program" does not necessarily refer to a compiled application, rather, any set of commands submitted for execution by a user or operator. Such "program" could include a script or job control stream
and any included calls to macro-instructions, system utilities
or application program modules. An entire, interactive, logged-in user session can be thought of as a "program" in this sense.
A program generally comprises numerous tasks, a task being a relatively small group of processor instructions which together achieve a definable logical step in the completion of a job or the execution of a continuous-running application program. A task frequently ends with some request requiring the moving of data, a convenient opportunity to allow another program to have system resources, particularly CPU time
.
In multiprogramming, concurrent running (sharing of the processor) is achieved when the operating system identifies opportunities to interrupt the handling of one program between tasks (e.g., when it is waiting for input/output) and to transfer process control to another program (application, job or user). To a great extent, the ability of a system to share its resources equitably—or according to certain priorities—is dependent upon the design of the programs being handled and how frequently they may be interrupted.
Multi-tasking
eliminates that dependency and expands upon multiprogramming by enabling the operating system supervisor
to interrupt programs in the middle of tasks and to transfer processor control so rapidly that each program is now assured a portion of each processing second, making the interruptions imperceptible to most human-interactive applications.
Initially, this technology was sought in order to optimize use of a computer system, since time and processing resources were often wasted when a single job waited for human interaction was developed as a feature of operating systems in the late 1950s and came into common use in mainframe computing in the mid- to late 1960s. This followed the development of hardware systems that possessed the requisite circuit logic and instruction sets to facilitate the transfer of control between the operating system and one or more independent applications, users or job stream
Job stream
In an IBM mainframe, the job stream is the path of execution that a job follows. The JCL and any data submitted with it form the job stream. There can be multiple EXEC and DD statements in a job stream if a job involves more than one program....
s.
The use of multiprogramming was enhanced by the arrival of virtual memory
Virtual memory
In computing, virtual memory is a memory management technique developed for multitasking kernels. This technique virtualizes a computer architecture's various forms of computer data storage , allowing a program to be designed as though there is only one kind of memory, "virtual" memory, which...
and virtual machine
Virtual machine
A virtual machine is a "completely isolated guest operating system installation within a normal host operating system". Modern virtual machines are implemented with either software emulation or hardware virtualization or both together.-VM Definitions:A virtual machine is a software...
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, non-existent and invisible to them.
Multiprogramming should be differentiated from multi-tasking since not all multiprogramming entails—or has the capability for-- "true" multi-tasking. This is the case even though the use of multi-tasking generally implies the use of some multiprogramming methods.
In this context, the root word "program" does not necessarily refer to a compiled application, rather, any set of commands submitted for execution by a user or operator. Such "program" could include a script or job control stream
Job control
On operating systems that support executing multiple processes in parallel or in series , job control refers to the orchestration of multiple batch jobs.-Unix shell:...
and any included calls to macro-instructions, system utilities
System utility
The system utility may be defined in terms of the satisfaction of the system stakeholders.- Actual Utility :The actual utility is the actual stakeholders' satisfaction....
or application program modules. An entire, interactive, logged-in user session can be thought of as a "program" in this sense.
A program generally comprises numerous tasks, a task being a relatively small group of processor instructions which together achieve a definable logical step in the completion of a job or the execution of a continuous-running application program. A task frequently ends with some request requiring the moving of data, a convenient opportunity to allow another program to have system resources, particularly CPU time
CPU time
CPU time is the amount of time for which a central processing unit was used for processing instructions of a computer program, as opposed to, for example, waiting for input/output operations. The CPU time is often measured in clock ticks or as a percentage of the CPU's capacity...
.
In multiprogramming, concurrent running (sharing of the processor) is achieved when the operating system identifies opportunities to interrupt the handling of one program between tasks (e.g., when it is waiting for input/output) and to transfer process control to another program (application, job or user). To a great extent, the ability of a system to share its resources equitably—or according to certain priorities—is dependent upon the design of the programs being handled and how frequently they may be interrupted.
Multi-tasking
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
eliminates that dependency and expands upon multiprogramming by enabling the operating system supervisor
Supervisory program
A supervisory program or supervisor is a computer program, usually part of an operating system, that controls the execution of other routines and regulates work scheduling, input/output operations, error actions, and similar functions and regulates the flow of work in a data processing system.It...
to interrupt programs in the middle of tasks and to transfer processor control so rapidly that each program is now assured a portion of each processing second, making the interruptions imperceptible to most human-interactive applications.