RSX11

RSX-11 is a family of real-time, multi-user operating systems developed by Digital Equipment Corporation (DEC) for the PDP-11 family of minicomputers. Introduced in the early 1970s, RSX-11 provided time-sharing capabilities on small to mid-range hardware, enabling multiple users to run concurrently with real-time input/output.

The RSX-11 family includes several variants, notably RSX-11A, RSX-11D, RSX-11M, and RSX-11S. RSX-11A established the core architecture for multi-user operation. RSX-11D added enhancements to the file system and I/O facilities. RSX-11M was the most widely deployed variant, offering more extensive memory management and broader device support for larger installations. RSX-11S was a compact version optimized for smaller PDP-11 systems and real-time control tasks.

Common features across RSX-11 variants include a real-time scheduler capable of supporting priority-based multitasking, interprocess communication, device drivers, and support for terminal-based time-sharing. It used the RMS-11 Record Management System file system for data storage and a set of system utilities and programming interfaces for task creation, synchronization, and debugging.

RSX-11 played a significant role in DEC’s real-time and multi-user strategy during the 1970s and into the 1980s, particularly in laboratory, manufacturing, and process-control environments. As UNIX-based systems and later DEC OpenVMS on newer hardware emerged, RSX-11's prominence declined, though RSX-11 environments remained in use in some installations for years.