RT11

RT-11 is a real-time operating system developed by Digital Equipment Corporation (DEC) for the PDP-11 family of minicomputers. Introduced in the early 1970s, it was designed for small, single-user real-time control applications and for interactive development in environments with a terminal connected to the PDP-11. RT-11 provided a compact, purpose-built environment suitable for instrumentation, process control, and testing tasks.

The operating system features a simple, priority-based scheduler paired with interrupt-driven I/O to support time-sensitive tasks. It offers multitasking across multiple user programs, with mechanisms for task communication and synchronization appropriate to its scale. RT-11 runs programs written for the PDP-11 and includes a command-oriented environment for loading, executing, and debugging code.

RT-11 includes its own file system and toolchain for managing programs and data on DEC disk drives of the era, such as RK05 and TK50. The system provides a basic command processor, utilities, and a text editor, enabling users to assemble, load, and run applications directly from the console. The footprint of RT-11 is small, designed to fit on modest memory configurations typical of early PDP-11 systems.

Historically, RT-11 occupied a niche as a compact, straightforward real-time OS distinct from DEC’s larger real-time offerings. It was eventually complemented and partly superseded by more feature-rich DEC real-time systems such as RSX-11, but RT-11 remained in use for many years in labs, education, and small-scale control environments due to its simplicity and reliability.

See also PDP-11, RSX-11, RT-11 File System.