View source for TSX-Plus

{{Short description|Software}}
{{Infobox OS
| name                   = TSX-Plus<!-- Name of program or distribution -->
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| developer              = S&H Computer Systems<!-- Name of main developer or sponsor-->
| family                 = <!-- "Unix-like" or "Microsoft Windows" -->
| working state          = <!-- "Current", "Discontinued" (operating systems), or "No longer supported" (releases) -->
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| update model           = <!-- APT, Windows Update, etc. -->
| package manager        = <!-- dpkg, rpm, Windows installer, etc. -->
| supported platforms    = [[PDP-11]]/[[LSI-11]]<!-- IA-32, x64, Itanium, ARM, etc. -->
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'''TSX-Plus''' is a [[multi-user]] [[operating system]] for the [[PDP-11]]/[[LSI-11]] series of computers. It was developed by [[S&H Computer Systems|S&H Computer Systems, Inc.]] and is based on [[Digital Equipment Corporation|DEC]]'s [[RT-11]] single-user [[real-time operating system]] (TSX-Plus installs on top of RT-11).

==Overview==
The system is highly configurable and tunable.{{Fact|date=February 2007}}

Due to the constraints of the memory management system in the PDP-11/LSI-11, the entire operating system core must occupy no more than 40 [[kibibyte]]s of memory, out of a maximum possible 4 [[mebibyte]]s of [[primary storage|physical memory]] that can actually be installed in those machines (mandated by the 22-bit [[address space]]). The strength of TSX-Plus is to simultaneously provide to multiple users the services of DEC's single-user [[RT-11]].<ref>{{cite magazine
   |magazine=Hardcopy  |title=The RT-11 Perspective
   |date=January 1985  |page=125 |author=Milton Campbell}}</ref> Depending on which PDP-11 model and the amount of memory, the system could support a minimum of 12 users<ref name=TSX32.DCLdialog>{{cite news
|newspaper=[[Computerworld]] |title=S&H TSX-Plus on 11/23, 11/34
|quote= efficient, general-purpose timesharing for up to 20 users on 11/23 and 11/34 based ...
|date=December 1, 1980  |page=67}}</ref> (14-18 users on a 2Mb 11/73, depending on workload). A productivity feature called "''virtual lines''" "allows a single user to control several tasks from a single terminal."<ref>{{cite magazine |magazine=Hardcopy |date=October 1982 |page=9 |title=TSX-Plus: Time Share RT-11}}</ref>

The software included a WP package named Lex-11<ref>See Tom Barnard and Ace Microsystems, Australia. New Scientist, 5 May 1983, Vol 98, No 1356, in Google Books.</ref> and a spreadsheet from [[Saturn Software]]. The machine slowed considerably if more than 8 students wanted to use the word-processing package at the same time. There was also a decision-table language called "D" from the NCC in Manchester which worked very well on TSX Plus.

==History==
Released in 1980, TSX-Plus was the successor to TSX, released in 1976.<ref name=TSX32.DCLdialog/> The system was popular in the 1980s. The last version of TSX-Plus had [[Internet protocol suite|TCP/IP]] support.

S&H wrote the original TSX because "Spending $25K on a computer that could only support one user bugged" (founder Harry Sanders); the outcome was the initial four-user TSX in 1976.<ref name=TSX32.DCLdialog/>

==Bootstrapping==
{{unreferenced section|date=October 2022}}
TSX-Plus required bootstrapping RT-11 first before running TSX-Plus as a user program. Once TSX-Plus was running, it would take over complete control of the machine from RT-11. It provided true memory protection for users from other users, provided user accounts and maintained account separation on disk volumes and implemented a superset of the RT-11 EMT programmed requests. RT-11 programs generally ran, unmodified, under TSX-Plus and, in fact, most of the RT-11 utilities were used as-is under TSX-Plus. Device drivers generally required only slight modifications.

==See also==
* [[TSX-32]]

==References==
{{Reflist}}

==External links==
*[https://web.archive.org/web/19961209114726/http://sandh.com/ S&H Homepage]

{{Operating system}}

[[Category:Proprietary operating systems]]
[[Category:PDP-11]]

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