HP-RT: HP’s real-time operating system from the ’90s

Every now and then I load OpenPA and browse around. Its creator and maintainer, Paul Weissmann, has been very active lately updating the site with new articles, even more information, and tons of other things, and it’s usually a joy to stumble upon something I haven’t read yet, or just didn’t know anything about. This time it’s something called HP-RT, a real-time operating system developed and sold by HP for a number of its PA-RISC workstations back in the ’90s.

HP-RT is derived from the real-time operating system LynxOS and was built as real-time operating system from scratch with native POSIX API and Unix features like protected address spaces, multiprocessing, and standard GUI. Real-time scheduling is part of the kernel with response times under 200 µs, later improved to sub-100 µs for uses such as hospital system tied to a heart monitor, or a missile tracking system.

For programming, HP-RT supported dynamic shared libraries, ANSI C, Softbench (5.2), FORTRAN, ADA, C++ and PA-RISC assembly. From HP-RT 3.0, GUI-based debugging environment (DDErt) and Event Logging library (ELOG) were included. POSIX 1003.1, 1003.1b and POSIX 1003.4a draft 4 were supported.

On the software side, HP-RT supported fast file system, X and Motif clients, X11 SERVERrt, STREAMSrt (SVR 3.2), NFS, and others.
↫ Paul Weissmann at OpenPA

I had no idea HP-RT existed, and looking at the feature list, it seems like it was actually a pretty impressive operating system and wider ecosystem back in the ’90s when it was current. HP released several versions of its real-time operating system, with 1997’s 3.0 and 3.01 being the final version. Support for it ended in the early 2000s alongside the end of the line for PA-RISC.

I’d absolutely love to try it out today, but sadly, my PA-RISC workstation – an HP Visualise c3750 – is way too “new” to be supported by HP-RT, and in the wrong product category at that. HP-RT required both a regular HP 9000 700 HP-UX workstation, as well as one of HP’s VME machines with a single-module module with the specific “rt” affix in the model number. On top of that you obviously needed the actual HP-RT operating system, which was part of the HP-RT Development Environment. The process entails using the HP-UX machine to compile HP-RT, which was then downloaded to the VMe machine.

The odds of not only finding all the right parts to complete the setup, but also to get it all working with what is undoubtedly going to be spotty documentation and next to nobody to talk to about how to do it, are very, very slim. I’m open to suggestions, of course, but considering the probable crazy rarity of the specific hardware, the price-gauging going on in the retrocomputing world, the difficulty of shipping to the Swedish Arctic, and the knwoledge required, I don’t think I’ll be the one to get this to work and show it off.

But man do I want to.