TSX-Plus is a multi-user

Multi-user

Multi-user is a term that defines an operating system or application software that allows concurrent access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving the...

 operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 for the PDP-11

PDP-11

The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...

/LSI-11 series of computers. It was developed by S&H Computer Systems, Inc. and is based on DEC

Digital Equipment Corporation

Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

's RT-11

RT-11

RT-11 was a small, single-user real-time operating system for the Digital Equipment Corporation PDP-11 family of 16-bit computers...

 single-user real-time operating system

Real-time operating system

A real-time operating system is an operating system intended to serve real-time application requests.A key characteristic of a RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task; the variability is jitter...

 (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 kibibyte

Kibibyte

The kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 1024; therefore, 1 kibibyte is . The unit symbol for the kibibyte is KiB. The unit was established by the International Electrotechnical Commission in 1999 and has been accepted for use...

s of memory, out of a maximum possible 4 mebibyte

Mebibyte

The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220, therefore 1 mebibyte is . The unit symbol for the mebibyte is MiB. The unit was established by the International Electrotechnical Commission in 2000 and has been accepted for use by all major...

s of physical memory that can actually be installed in those machines (mandated by the 22-bit address space

Address space

In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...

). Despite these limitations, TSX-Plus is actually able to service up to about 30 simultaneous users while still maintaining decent response times.

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.

The system was popular in the 1980s, although had a major number of clones. The latest version of TSX-Plus has TCP/IP

Internet protocol suite

The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...

support. The system is still in use and supported.