TSX Plus: Многопользовательская ОС для PDP 11/LSI 11

Software

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).

The system is highly configurable and tunable. 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. Depending on which PDP 11 model and the amount of memory, the system could support a minimum of 12 users (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." 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.

Released in 1980, TSX Plus was the successor to TSX, released in 1976. 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.

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.