TSX-Plus

{{Short description|Software}} {{Infobox OS | name = TSX-Plus | logo =  | logo caption = | logo size = | logo alt = | screenshot =  | caption = | screenshot_size = | screenshot_alt = | collapsible = | version of =  | developer = S&H Computer Systems | family =  | working state =  | source model =  | released = | discontinued =  | RTM date =  | GA date =  | latest release version = | latest release date = | latest preview version = | latest preview date =  | marketing target = | programmed in = | language = English | update model =  | package manager =  | supported platforms = PDP-11/LSI-11 | kernel type =  | userland = | ui = | license = Proprietary | preceded by = | succeeded by = | website =  | support status =  | other articles = | prog_language = }} '''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, Inc. and is based on 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 kibibytes of memory, out of a maximum possible 4 mebibytes of 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 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]

Category:Proprietary operating systems Category:PDP-11