TSX-Plus
| Industry | Computer software |
|---|---|
| Founded | 1976 |
| Founder | Harry Sanders |
| Products | TSX, TSX-Plus |
TSX-Plus is a multi-user operating system designed for the PDP-11/LSI-11 family, created by S&H Computer Systems, Inc.. It functions as an overlay on Digital Equipment Corporation's RT-11, which is a single-user real-time operating system.
Overview
Optimized for the limited memory environment of PDP-11/LSI-11 machines, TSX-Plus is highly adaptable and maintains a compact OS core that occupies less than 40 kibibytes within a 22-bit address space capable of addressing up to 4 mebibytes of physical RAM. Its primary advantage lies in allowing multiple users to simultaneously work within DEC's originally single-user RT-11 system. Depending on the hardware configuration and available memory, TSX-Plus can accommodate between 12 and 18 active users at once, with some setups efficiently supporting as many as 20.
A significant enhancement called virtual lines enables individual users to handle several tasks concurrently from a single terminal, thereby improving multitasking efficiency. The software package included Lex-11, a word processing application, along with a spreadsheet program developed by Saturn Software. However, when more than eight users accessed the word processor simultaneously, system responsiveness decreased. Additionally, TSX-Plus supported the "D" decision-table language from the NCC in Manchester, which ran effectively on this platform.
History
TSX-Plus was introduced in 1980 as the successor to TSX, which had debuted in 1976. It enjoyed widespread use throughout the 1980s, with its last release incorporating support for the TCP/IP. Harry Sanders, the creator of the original TSX, developed it to provide multi-user functionality on machines that had previously only supported single-user operations, fulfilling an important market demand.
Bootstrapping
The operation of TSX-Plus begins by loading RT-11, after which TSX-Plus starts as a user-level program that assumes complete control over the hardware. It delivers genuine memory protection, manages user accounts with isolated disk access, and extends RT-11's EMT (emulator trap) requests. The majority of RT-11 applications and utilities run under TSX-Plus without modification, requiring only minimal adjustments to device drivers.