PA-RISC information - since 1999

No RISC No Fun

OpenPA is an independent technical resource on HP 9000 and PA-RISC computers and operating systems. Information on PA-RISC is contained in more than 100 articles published on OpenPA since 1999 on HP 9000 computers, PA-RISC architecture and software ecosystem:

  1. Hardware: Technology covered by this site is based on HP PA-RISC architecture and processors from the 1980s to 2000s. Most of the chipsets and system designs used were custom HP for its PA-RISC servers and workstations.
  2. Computers: Many different PA-RISC computers were produced between the 1980s and 2000s, the majority from HP in its HP 9000 range of servers, workstations and mainframes. Over 245 systems covered on OpenPA.
  3. Operating: A broad range of Unix operating systems has been available since 1986 for HP 9000 and PA-RISC workstations and servers, from HP-UX to Mach and BSD, as commercial products, open source ports and and R&D projects.

Sources used on OpenPA are mostly PA-RISC technical reference manuals, HP handbooks and architecture documents, correlated with articles and news releases – many disappeared lately. OpenPA is independent of and does not represent HP in any way. Read also the OpenPA book.

Convex SPP/UX Mach on PA-RISC operating system

By Paul Weissmann on 6 February 2024

Convex SPP1200
© Convex 1994

The Exemplar Operating System SPP-UX, was a scalable Unix based on Mach developed by Convex for its SPP1000 and SPP2000 mainframe computers with up to 128 or 512 processors.

The Convex Exemplar SPP were scalable PA-RISC mainframes, released by Convex in 1994 after using custom Convex processors. SPP-UX was the distributed architecture operating system for the SPPs that was supposed to look like (emulate) HP-UX for developers but was very different below the userland.

Convex and HP started collaborating around the early 1990s, from joint cluster-computing solutions based on HP 9000 in 1992, HP licensing HP-UX to Convex in 1993 and finally HP becoming a value-added reseller (VAR) for Convex before acquiring the company outright in 1995. The SPPs were quickly taken into the HP portfolio.

The SPP-UX kernel and architecture was based on a Mach 3.0 distributed microkernel and was taken over by HP during the acquisition of Convex and its Exemplar SPP computers. Each hypernode of the SPP computers ran an independent instance of the Mach microkernel There were three (four) main layers for SPP-UX:

  1. Distributed kernel: Based on an enhanced Mach 3.0 microkernel, supposedly OSF 1/AD Mach from OSF RI, that was targeted for coupled SMP systems to support highly parallel applications; message-passing paradigm for NUMA computers
  2. HP-UX compatibility: Second operating system layer compatible to HP-UX, to enable running HP-UX applications on SPP-UX, supposedly emulated HP-UX APIs and ABIs; management of distributed resources, processors, simultaneous users, process scheduler; supported parallel jobs as well as multiprocessing of single-thread
  3. Extensions and features: Central management, open systems and standards like POSIX, specialized programming and development environment
  4. Lastly, the applications: Possible were HP Series 700 (stock HP-UX), C Series and MPP applications

HP i2000 – The first and unloved HP Itanium workstation

By Paul Weissmann on 16 January 2024

In 2001, HP released the HP i2000 Itanium workstation with first generation Merced processors as proof-of-concept to finally deliver first Itaniums with an Intel 82460GX reference design. IA64, Itanium had long been in development as joint HP-Intel project that promised a better CPU future as a VLIW/EPIC architecture running HP-UX, Windows and Linux.

HP i2000
© Hewlett Packard 2001

As HP described the Itanium genesis in 2001, HP invited Intel into our lab, we showed them the architecture that will become the pervasive 64-bit architecture of the 21st century. They shared our vision and together we invented the Itanium processor family specification. HP i2000 was the first, unhappy materialization of that vision.

It was the first Itanium workstation to actually leave the gates of HP, in parallel to sunset PA-RISC workstations C3650 and C3750. At the time Unix and RISC workstations were on their way out in the industry due to price and competition from off-the-shelf PCs running Windows NT.

The HP i2000 with first generation Itanium (Merced) CPU was beaten by most contemporary workstations of the early 2000s in benchmarks other than FP. While the i2000 had a SPEC2000 integer score of 335, the contemporary C3700 workstation had a SPEC2000 of 604 while the last c8000 PA-RISC workstation achieved a SPEC2000 int of 1001.

HP claimed in 2001 that while the i2000 will outperform most, if not all, current architectures in floating point performance in the SPECfp benchmark its more real-world relevant Integer performance in applications such as encryption/decryption operations for secure web serving is excellent. HP-UX support for the HP i2000 was limited to a single release, HP-UX 11i v1.5.

So many HP-UX Unix releases on PA-RISC

By Paul Weissmann on 11 January 2024

HP-UX is HP’s commercial Unix operating system for its PA-RISC workstations and servers. First released during the 1980s for the earliest PA-RISC servers and their predecessors, there were many different HP-UX releases and versions since 1982. Most of them ran on PA-RISC, though exactly which is complicated to find out after all these years. We took 25 years to do it.

© Hewlett Packard from the 1980s

First HP-UX 1.0 was released in 1983 for HP FOCUS and was supposedly very different to other HP-UX versions, based on an AT&T Unix kernel. There was another HP-UX 1.0 in 1984 for the HP Integral PC (on ROM) before HP-UX 1.0 for PA-RISC in 1986.

HP-UX was released in different versions on PA-RISC, starting with 1.0 in 1986 on the first HP 9000 840, followed by 2.0 (1987), 3.0 (1988) and then 7.0 (1989 and 1990) for most of the 32-bit PA-RISC 1.0 servers.

HP-UX 8 was HP’s Unix for the new 32-bit PA-7000 and PA-7100 computers released in 1991. Codebases for HP 9000 700s workstations and 800s servers were different in HP-UX 8 with separate releases (even/odd).


HP-UX 9 was the second major release for PA-RISC workstations and supported most HP 9000 Series 700 workstations well. Until version 9, released in 1992, HP-UX was BSD Unix influenced and close to HPBSD, from 10 onward HP-UX became more System V Unix (SVR4) flavoured. Releases up to 9.0 and 10.10 were not Y2K-ready so HP offered an upgrade path to HP-UX 11 and exchange CDs for affected systems and license holders. This was a lifeline for many (second-hand) PA-RISC systems that easily transitioned to a rather modern operating system.

HP-UX 10.20 Spans the Full Range of HP 9000 Servers
and Workstations
© Hewlett Packard 2000

HP-UX 10.20 from 1996 was quite popular in the late 1990s to early 2000s with good performance and support for most PA-RISC systems. It was the last 32-bit-only HP-UX and had different releases for HP 9000 700 workstations and HP 9000 800 servers, HP-UX 11.00 and later had unified releases for servers and workstations. Extensions packs and ACEs added hardware support for many newer PA-RISC, including newer 64-bit computers (in 32-bit).

Version 11.00 of HP-UX was the first 64-bit HP Unix, released in 1997. It ran on both 32-bit and 64-bit PA-RISC computers and supported most lettered servers and workstations plus some older 700s and 800s systems. It was sponsored by the HP Server group and thus focused on PA-RISC servers initially – support for workstation and graphics was added later. HP-UX 11i is last of the line for HP Unix, it supported PA-RISC and introduced Itanium support. It was first released in 2000 and developed and extended into different streams over the years (PA-RISC, Itanium).

There were many other minor and major HP-UX releases for different classes of HP computers. It's all a bit hazy, especially with versions from the 1980s and the later changes around Itanium.

Real-time computing on PA-RISC with HP-RT

By Paul Weissmann on 8 January 2024

HP-RT was a real-time operating system from HP for its HP 9000 740 VME instrumentation computers, released from 1993 to 1997 in six versions from 1.0 to 3.0. It apparently was (also) sold as part of the HP-RT Developer's Kit that included the 743rt and high performance 744rt VME computers.

© Hewlett Packard, HP Journal

Based on LynxOS, HP-RT was built as a real-time operating system from scratch, with a native POSIX API and included Unix features such as protected address spaces, multiprocessing, and standard GUI. Real-time scheduling is part of the kernel with response times under 200 µs. It supported most of the on-board hardware and only few HP expansion devices.

On the software side, HP-RT supported fast file system, X and Motif clients, X11 SERVERrt, STREAMSrt (SVR 3.2), NFS,

© Hewlett Packard, HP Journal

Software development on HP-RT required the HP-RT Development Environment, 740rt VME machines, like the 742rt, but also a dedicated HP 9000 700 host machine running HP-UX for compiling and linking. The software was then downloaded to the rt VME system.

There were six versions of HP-RT from 1.0 to 3.01 plus several minor patch releases. A break in releases was between 2.1 (1995) and 3.0 (1997) when support had to be provided for HP-UX 9 as well as the new HP-UX 10 in the HP-RT developers kit.

HP 74x VME products such as 743i and 744 were discontinued in 2002 as customers have migrated to new solutions and platforms more rapidly than anticipated with end of support between 2003 and 2007. This included HP-RT as there were no follow-on HP PA-RISC products.

Windows NT and NetWare were ported to PA-RISC

By Paul Weissmann on 4 January 2024

Besides the well known commercial PA-RISC operating systems and research projects based on Unix and Mach, several rather odd operating system choices were ported to PA-RISC over the years. Forgotten since, a few diverse corporate development projects targeted PA-RISC for commercial operating systems throughout the 1990s – with mixed results.


HP undertook efforts in the mid-1990s to port Microsoft Windows NT to PA-RISC in order to hedge their bets in the workstation and NT markets. While pursuing a PA-RISC port, HP modified the PA-RISC architecture for bi-endianess and even conducted a back-room presention in 1994 of a PA-7100LC workstation running Windows NT.

Reports of a Windows NT port continued through 1994 and 1995 but sources at HP soon spoke of dim prospects for NT on PA-RISC and a dead-end architecture with a seeming consensus of a post-RISC (Itanium) future around the corner. NT supported a few RISC architectures for a while, but not PA-RISC.


In the same era, a port of NetWare to PA-RISC was undertaken by HP and Novell for Processor-Independent NetWare (PIN). NetWare 4.1 was slated to support a variety of RISC architectures such as Alpha, Sun, MIPS and PowerPC. However, development at Novell for PIN on PA-RISC took longer than planned, and HP finally pulled out in 1994 after Novell was unable to deliver Processor-Independent NetWare (PIN) on schedule.

Apparently there was also a prototype of HP-UX on x86 hardware a few years later, when the future of HP-UX and its sole surving platform Itanium came in doubt during the early 2010s. PA-RISC was long gone by then and HP started hedging their bets and experimenting with Unix platforms, as the writing had been on the wall for Itanium for a while.

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