RT11
| Developer | Digital Equipment Corporation and Mentec Inc. |
|---|---|
| Written in | MACRO-11 |
| OS family | DEC OS family |
| Working state | Discontinued |
| Source model | Closed source |
| Initial release | 1970 |
| Latest release | 5.7 / October 1998 |
| Marketing target | Laboratory/Scientific/Real-time industrial equipment |
| Available in | English |
| Platforms | PDP-11 family and clones |
| Kernel type | Monolithic kernel |
| Default user interface | Keyboard Monitor (KMON) Command line interface |
| License | Proprietary |
RT-11 ("RT" for real-time) is a discontinued small, single-user real-time operating system for the Digital Equipment Corporation PDP-11 family of 16-bit computers. RT-11 was first implemented in 1970 and was widely used for real-time systems, process control, and data acquisition across the full line of PDP-11 computers.
RT-11 systems did not support preemptive multitasking, but most versions could run multiple simultaneous applications. All variants of the monitors provided a background job. The FB, XM and ZM monitors also provided a foreground job, as well as six system jobs if selected via the SYSGEN system generation program. These tasks had fixed priorities, with the background job lowest and the foreground job highest. It was possible to switch between jobs from the system console user interface, and SYSGEN could generate a monitor that provided a single background job (the SB, XB and ZB variants).
RT-11 was written in assembly language. Heavy use of the conditional assembly and macro programming features of the MACRO-11 assembler allowed a significant degree of configurability and allowed programmers to specify high-level instructions otherwise unprovided for in machine code. RT-11 distributions included the source code of the operating system and its device drivers with all the comments removed and a program named "SYSGEN" which would build the operating system and drivers according to a user-specified configuration. Developer's documentation included a kernel listing that included comments.
In RT-11, device drivers were loadable, except that prior to V4.0 the device driver for the system device (boot device) was built into the kernel at configuration time. Because RT-11 was commonly used for device control and data acquisition, it was common for developers to write or enhance device drivers. DEC encouraged such driver development by making their hardware subsystems (from bus structure to code) open, documenting the internals of the operating system, encouraging third-party hardware and software vendors, and by fostering the development of the Digital Equipment Computer Users Society.
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