THE multiprogramming system - Revision history

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v2.05 - Fix errors for CW project (External link with two brackets)

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	The '''THE multiprogramming system''' or '''THE OS''' was a computer [[operating system]] designed by a team led by [[Edsger W. Dijkstra]], described in monographs in 1965-66<ref name="ewd196">		The '''THE multiprogramming system''' ('''THE OS''') was a computer [[operating system]] designed by a team led by [[Edsger W. Dijkstra]], described in monographs in 1965-66<ref name="ewd196">
	{{Cite EWD\|196\|The structure of the 'THE'-multiprogramming system}} (Jun 14, 1965)		{{Cite EWD\|196\|The structure of the 'THE'-multiprogramming system}} (Jun 14, 1965)
	</ref> and published in 1968.<ref>		</ref> and published in 1968.<ref>
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	\|date=May 1988		\|date=May 1988
	\| page = 512		\| page = 512
	}}</ref> that supported [[~~Computer~~ multitasking\|multitasking]]; it was not designed as a [[multi-user]] operating system. It was much like the [[SDS 940]], but "the set of [[process (computing)\|process]]es in the THE system was static".<ref name="osc"/>		}}</ref> that supported [[computer multitasking\|multitasking]]; it was not designed as a [[multi-user]] operating system. It was much like the [[SDS 940]], but "the set of [[process (computing)\|process]]es in the THE system was static".<ref name="osc"/>

	The THE system apparently introduced the first forms of software-based [[~~Memory~~ page\|paged]] [[virtual memory]] (the [[Electrologica X8]] did not support [[~~Memory~~ management unit\|hardware-based]] [[memory management]]),<ref name="osc"/> freeing programs from being forced to use physical locations on the [[drum memory]]. It did this by using a modified [[ALGOL]] [[compiler]] (the only [[programming language]] supported by Dijkstra's system) to "automatically generate [[~~System~~ call\|calls to system routines]], which made sure the requested information was in memory, [[~~Swap~~ memory\|swapping]] if necessary".<ref name="osc"/> Paged virtual memory was also used for [[~~Data~~ buffer\|buffering]] [[input/output]] (I/O) device data, and for a significant portion of the operating system code, and nearly all the [[ALGOL 60]] compiler. In this system, [[~~Semaphore~~ (programming)\|semaphores]] were used as a programming construct for the first time.		The THE system apparently introduced the first forms of software-based [[memory page\|paged]] [[virtual memory]] (the [[Electrologica X8]] did not support [[memory management unit\|hardware-based]] [[memory management]]),<ref name="osc"/> freeing programs from being forced to use physical locations on the [[drum memory]]. It did this by using a modified [[ALGOL]] [[compiler]] (the only [[programming language]] supported by Dijkstra's system) to "automatically generate [[system call\|calls to system routines]], which made sure the requested information was in memory, [[swap memory\|swapping]] if necessary".<ref name="osc"/> Paged virtual memory was also used for [[data buffer\|buffering]] [[input/output]] (I/O) device data, and for a significant portion of the operating system code, and nearly all the [[ALGOL 60]] compiler. In this system, [[semaphore (programming)\|semaphores]] were used as a programming construct for the first time.

	==Design==		==Design==
	The design of the THE multiprogramming system is significant for its use of a [[~~Abstraction~~\|layered structure]], in which "higher" layers depend on "lower" layers only:		The design of the THE multiprogramming system is significant for its use of a [[abstraction\|layered structure]], in which "higher" layers depend on "lower" layers only:
	* '''Layer 0''' was responsible for the multiprogramming aspects of the operating system. It decided which process was allocated to the [[central processing unit]] (CPU), and accounted for processes that were blocked on ~~[[Semaphore (programming)\|~~semaphores]]. It dealt with [[interrupt]]s and performed the [[context switch]]es when a process change was needed. This is the lowest level. In modern terms, this was the [[scheduler]].		* '''Layer 0''' was responsible for the multiprogramming aspects of the operating system. It decided which process was allocated to the [[central processing unit]] (CPU), and accounted for processes that were blocked on semaphores. It dealt with [[interrupt]]s and performed the [[context switch]]es when a process change was needed. This is the lowest level. In modern terms, this was the [[scheduler]].
	* '''Layer 1''' was concerned with [[~~Memory~~ management\|allocating memory]] to processes. In modern terms, this was the pager.		* '''Layer 1''' was concerned with [[memory management\|allocating memory]] to processes. In modern terms, this was the pager.
	* '''Layer 2''' dealt with communication between the operating system and the [[system console]].		* '''Layer 2''' dealt with communication between the operating system and the [[system console]].
	* '''Layer 3''' managed all I/O between the devices attached to the computer. This included buffering information from the various devices.		* '''Layer 3''' managed all I/O between the devices attached to the computer. This included buffering information from the various devices.
	* '''Layer 4''' consisted of [[~~User~~ space\|user programs]]. There were 5 processes: in total, they handled the [[~~Compiler~~\|compiling]], [[~~Execution~~ (computing)\|executing]], and [[~~Printer~~ (computing)\|printing]] of user programs. When finished, they [[~~Control~~ flow\|passed control]] back to the schedule [[~~Queue~~ (abstract data type)\|queue]], which was [[~~Priority~~ queue\|priority-based]], favoring recently started processes and ones that blocked because of I/O.		* '''Layer 4''' consisted of [[user space\|user programs]]. There were 5 processes: in total, they handled the [[compiler\|compiling]], [[execution (computing)\|executing]], and [[printer (computing)\|printing]] of user programs. When finished, they [[control flow\|passed control]] back to the schedule [[queue (abstract data type)\|queue]], which was [[priority queue\|priority-based]], favoring recently started processes and ones that blocked because of I/O.
	* '''Layer 5''' was the user; as Dijkstra notes, "not implemented by us".		* '''Layer 5''' was the user; as Dijkstra notes, "not implemented by us".

	The constraint that higher layers can only depend on lower layers was imposed by the designers in order to make reasoning about the system (using quasi-[[formal methods]]) more tractable, and also to facilitate building and testing the system incrementally. The layers were implemented in order, layer 0 first, with thorough testing of the abstractions provided by each layer in turn. This division of the [[kernel (operating system)\|kernel]] into layers was similar in some ways to [[Multics]]' later [[protection ring\|ring-segmentation]] model. Several subsequent operating systems have used layering to some extent, including [[Windows NT]] and [[macOS]], although usually with fewer layers.		The constraint that higher layers can only depend on lower layers was imposed by the designers in order to make reasoning about the system (using quasi-[[formal methods]]) more tractable, and also to facilitate building and testing the system incrementally. The layers were implemented in order, layer 0 first, with thorough testing of the abstractions provided by each layer in turn. This division of the [[kernel (operating system)\|kernel]] into layers was similar in some ways to [[Multics]]' later [[protection ring\|ring-segmentation]] model. Several subsequent operating systems have used layering to some extent, including [[Windows NT]] and [[macOS]], although usually with fewer layers.

	The code of the system was written in [[assembly language]] for the Dutch [[Electrologica X8]] computer. This computer had a [[word (computer architecture)\|word]] size of 27 bits, 48 [[kiloword]]s of [[core memory]],<ref name="osc"/> 512 kilowords of [[drum memory]] providing [[cache (computing)\|backing store]] for the [[~~Cache~~ replacement policies\|LRU cache algorithm]], paper tape readers, paper tape punches, plotters, and printers.		The code of the system was written in [[assembly language]] for the Dutch [[Electrologica X8]] computer. This computer had a [[word (computer architecture)\|word]] size of 27 bits, 48 [[kiloword]]s of [[core memory]],<ref name="osc"/> 512 kilowords of [[drum memory]] providing [[cache (computing)\|backing store]] for the [[cache replacement policies\|LRU cache algorithm]], paper tape readers, paper tape punches, plotters, and printers.

	==See also==		==See also==
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	* [[Ring (computer security)]]		* [[Ring (computer security)]]
	* [[Timeline of operating systems]]		* [[Timeline of operating systems]]
	* Source code is available at http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-1-pdf/k-1-C1063.6-source-THE-os.pdf

	==References==		==References==
	{{Reflist}}		{{Reflist}}

			==External links==
			* [http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-1-pdf/k-1-C1063.6-source-THE-os.pdf Source code is available]

	{{Edsger Dijkstra}}		{{Edsger Dijkstra}}

2600:1700:5450:BF70:C68:2EDE:2970:C259: /* See also */

2023-11-08T17:19:33Z

See also

New page

{{Short description|First implementation of paged virtual memory}}
{{Infobox OS
| name = THE multiprogramming system
| logo = 
| logo size =
| logo caption =
| logo alt =
| screenshot = 
| caption =
| developer = [[Eindhoven University of Technology]] (Technische Hogeschool Eindhoven);<br/>[[Edsger Dijkstra]], ''et al.''
| family =
| working state = Discontinued
| source model =
| released = {{Start date and age|1965}}
| discontinued = Yes
| latest release version = Final
| latest release date = {{Start date and age|1968}}
| marketing target = [[Research]]
| programmed in = [[Electrologica X8]] [[assembly language]]
| language = English
| update model = Compile from [[source code]]
| supported platforms = [[Electrologica X8]]
| kernel type = [[Operating system abstraction layer|Layered]]
| userland =
| ui = [[Paper tape]]
| license =
| preceded by =
| succeeded by =
| website = 
}}
The '''THE multiprogramming system''' or '''THE OS''' was a computer [[operating system]] designed by a team led by [[Edsger W. Dijkstra]], described in monographs in 1965-66<ref name="ewd196">
{{Cite EWD|196|The structure of the 'THE'-multiprogramming system}} (Jun 14, 1965)
</ref> and published in 1968.<ref>
{{Citation
|last=Dijkstra
|first=E.W.
|author-link=Edsger W. Dijkstra
|title=The structure of the 'THE'-multiprogramming system
|journal=Communications of the ACM
|volume=11
|issue=5
|pages=341–346
|year=1968
|doi=10.1145/363095.363143
|s2cid=2021311
|doi-access=free
}}
</ref>
Dijkstra never named the system; "THE" is simply the abbreviation of "Technische Hogeschool Eindhoven", then the name (in [[Dutch language|Dutch]]) of the [[Eindhoven University of Technology]] of the [[Netherlands]]. The THE system was primarily a [[batch system]]<ref name="osc">{{Citation
| title = Operating System Concepts
| last1 = Silberschatz
| first1 = Abraham
| last2 = Peterson
| first2 = James L.
| chapter = 13: Historical Perspective
|date=May 1988
| page = 512
}}</ref> that supported [[Computer multitasking|multitasking]]; it was not designed as a [[multi-user]] operating system. It was much like the [[SDS 940]], but "the set of [[process (computing)|process]]es in the THE system was static".<ref name="osc"/>

The THE system apparently introduced the first forms of software-based [[Memory page|paged]] [[virtual memory]] (the [[Electrologica X8]] did not support [[Memory management unit|hardware-based]] [[memory management]]),<ref name="osc"/> freeing programs from being forced to use physical locations on the [[drum memory]]. It did this by using a modified [[ALGOL]] [[compiler]] (the only [[programming language]] supported by Dijkstra's system) to "automatically generate [[System call|calls to system routines]], which made sure the requested information was in memory, [[Swap memory|swapping]] if necessary".<ref name="osc"/> Paged virtual memory was also used for [[Data buffer|buffering]] [[input/output]] (I/O) device data, and for a significant portion of the operating system code, and nearly all the [[ALGOL 60]] compiler. In this system, [[Semaphore (programming)|semaphores]] were used as a programming construct for the first time.

==Design==
The design of the THE multiprogramming system is significant for its use of a [[Abstraction|layered structure]], in which "higher" layers depend on "lower" layers only:
* '''Layer 0''' was responsible for the multiprogramming aspects of the operating system. It decided which process was allocated to the [[central processing unit]] (CPU), and accounted for processes that were blocked on [[Semaphore (programming)|semaphores]]. It dealt with [[interrupt]]s and performed the [[context switch]]es when a process change was needed. This is the lowest level. In modern terms, this was the [[scheduler]].
* '''Layer 1''' was concerned with [[Memory management|allocating memory]] to processes. In modern terms, this was the pager.
* '''Layer 2''' dealt with communication between the operating system and the [[system console]].
* '''Layer 3''' managed all I/O between the devices attached to the computer. This included buffering information from the various devices.
* '''Layer 4''' consisted of [[User space|user programs]]. There were 5 processes: in total, they handled the [[Compiler|compiling]], [[Execution (computing)|executing]], and [[Printer (computing)|printing]] of user programs. When finished, they [[Control flow|passed control]] back to the schedule [[Queue (abstract data type)|queue]], which was [[Priority queue|priority-based]], favoring recently started processes and ones that blocked because of I/O.
* '''Layer 5''' was the user; as Dijkstra notes, "not implemented by us".

The constraint that higher layers can only depend on lower layers was imposed by the designers in order to make reasoning about the system (using quasi-[[formal methods]]) more tractable, and also to facilitate building and testing the system incrementally. The layers were implemented in order, layer 0 first, with thorough testing of the abstractions provided by each layer in turn. This division of the [[kernel (operating system)|kernel]] into layers was similar in some ways to [[Multics]]' later [[protection ring|ring-segmentation]] model. Several subsequent operating systems have used layering to some extent, including [[Windows NT]] and [[macOS]], although usually with fewer layers.

The code of the system was written in [[assembly language]] for the Dutch [[Electrologica X8]] computer. This computer had a [[word (computer architecture)|word]] size of 27 bits, 48 [[kiloword]]s of [[core memory]],<ref name="osc"/> 512 kilowords of [[drum memory]] providing [[cache (computing)|backing store]] for the [[Cache replacement policies|LRU cache algorithm]], paper tape readers, paper tape punches, plotters, and printers.

==See also==
* [[RC 4000 Multiprogramming System]]
* [[Ring (computer security)]]
* [[Timeline of operating systems]]
* Source code is available at http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-1-pdf/k-1-C1063.6-source-THE-os.pdf

==References==
{{Reflist}}

{{Edsger Dijkstra}}

[[Category:Assembly language software]]
[[Category:Discontinued operating systems]]
[[Category:Dutch inventions]]
[[Category:Computer science in the Netherlands]]
[[Category:Information technology in the Netherlands]]
[[Category:Edsger W. Dijkstra]]
[[Category:1968 software]]