TSX-Plus

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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, Inc. and is based on DEC's RT-11 single-user real-time OS (that is, TSX-Plus installs on top of RT-11). The system is highly configurable and tunable.^{[citation needed]}

The system is interesting because, 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). Despite these limitations, TSX-Plus is actually able to service up to about 30 simultaneous users while still maintaining decent response times.^{[citation needed]} I used an lsi-11 with TSX-plus and 16 terminals in 1985-1987. The software included a WP package named Lex-11 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. It was very popular in the 1980s, and had a lot of clones. Latest version of TSX-Plus have TCP/IP support. The system is still in use and supported.

S&H Homepage: http://www.sandh.com/