PA-RISC information - since 1999

PA-RISC Operating Systems History


The history of PA-RISC operating systems began in parallel to the design and development of PA-RISC and HP 9000 computers. Many Unix and R&D operating systems were available in the late-1980s, first early commercial HP-UX for PA-RISC releases, followed by a plethora of research and development projects in the 1990s around Mach microkernel and BSD Unix versions which laid the basis for Linux and BSD ports of the 2000s.


HP-UX: The story of HP-UX Unix began before PA-RISC with versions for the early HP 9000 lineup — the HP FOCUS systems. From the late 1980s on, HP-UX was available on the first PA-RISC server computers (800s), with HP-UX 1.0 or 2.0 the first release on PA-RISC in 1986 or 1987.

Many updates soon followed, even though versioning was a bit complicated during that sparsely documented time. In the 1980s, another HP-UX was released with 3.0, followed by HP-UX 7.0 in 1990. The first HP Unix release that supported both 800 Series servers and the new 700 Series workstation was HP-UX 8.0 and then 9.0 from the early 1990s, still strongly BSD-based.

©1997 HP, from

The new HP-UX 10 was released a few years later in 1995, followed in quick sucession by 10.20 and 10.30. Due to feared Y2K issues in earlier versions, HP made HP-UX 10.20 available free of charge for HP 9000 owners for a while. A server-only 10.30 released followed in 1997, as were many Additional Core Enhancements (ACEs), that added workstation hardware support to HP-UX 10.20.

The modernized HP-UX 11.0 was released soon after, starting in 1997, with a true 64-bit kernel with full 64-bit support for 64-bit computers but still support for many 32-bit PA-RISC systems. There was supposedly scant support for workstations in the original 11.00 release that was developed by the HP Server division – to be added later with the EP and ACE in 1998 and 1999.

The focus of HP-UX shifted with 11i to the newer lettered (A-Class, B-Class, ...) and rp/rx 64-bit and Itanium servers. HP started developing the HP-UX kernel to support PA-RISC and Itanium already beginning in 1997, and apparently together with NEC and Hitachi, old PA-RISC co-conspirators. HP-UX 11i v2 from 2003 then integrated PA-RISC and Itanium into a single operating system stream while HP-UX was focused more and more on specialized server roles – and stopped supporting most older PA-RISC workstations and 32-bit servers too.

NexTSTEP 3.3
© NeXT 1994

NeXTSTEP: NeXTSTEP on PA-RISC was a commercial Mach-based operating system from the 1990s with an Unix userland and an extremely modern GUI. It was ported to PA-RISC in 1994 with version 3.3 developed specifically for the HP 9000 712 pizzabox workstation. Originally introduced in 1989, NeXTSTEP supported black (NeXT) and white (Intel) hardware, with support for RISC platforms including Sun SPARC and HP PA-RISC added in 3.3. Support for PA-RISC in NeXTSTEP was only brief and limited to a select set of 32-bit HP 9000 workstations.

NeXTSTEP itself, while revolutionary in aspects, did not have long commercial success. However some of its ideas and technologies live on though in Mac OS, after corporate consolidation in the tech sector. NeXTSTEP on HP 9000 712 workstations was a rather unique and modern operating system experience for the 90s.

Mainframes: There were a few other notable operating systems that ran on PA-RISC. HP’s own MPE business mainframe operating system was ported from the HP 3000 CISC platform to PA-RISC with MPE/XL and MPE/iX, with several releases from 1988 to 2002.

Several third-party operating systems for PA-RISC mainframes were developed by companies for their own computers. This includes Convex SPP/UX, a heavily modified Mach-based operating system familiar to HP-UX but a completely different design for the Convex/HP Exemplar SPP line of mainframes. The fault-tolerant Continuum servers from Stratus were also shipped with either Stratus FTX, a System V Unix, or Stratos VOS, a transaction-processing oriented system.

PRO and East Asia: In the mid-1990s, as part of the Precision RISC Organisation, HP’s PA-RISC consortium, some Asian third-party PA-RISC OEMs started selling their own PA-RISC computers. These either made use of licensed HP-UX versions or their own custom developed operating systems – like Hitachi with HI-UX/WE2 and HI-UX/MPP or Samsung with SS-UX (?).

Oddballs: Besides the well known commercial PA-RISC operating systems and research projects, some interesting operating systems were ported to PA-RISC. Forgotten since, Windows NT and NetWare were ported to PA-RISC in the 1990s as development projects. HP-UX was ported to x86 as a development project to hedge their bets – with mixed results.

Another PA-RISC operating system by HP was HP-RT, a real-time operating system geared towards instrumentation use cases on HP 9000 740 series VME workstations that had a short-ish lifespan between 1993 and 1997, when customers have migrated to new solutions and platforms more rapidly than anticipated.

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Open Source

Linux: A native Linux port to PA-RISC was started in 1998 and gained momentum when HP started helping with equipment and documentation in 1999. The main Linux port quickly superseded the earlier Mach-based MkLinux. Because of HP’s assistance, the machines targeted at that time were newer than what other ports supported, like the A180, B180 and 64-bit PA 2.0 systems.

PA-RISC support was included in the mainstream kernel, and shipped with Debian and Gentoo distributions as official ports. During the 2010s however, support declined and development was scaled back, resulting in the eventual removal of PA-RISC from official distributions. PA-RISC Linux still has the broadest support for systems and hardware from the current open source efforts.

BSD: Work on an OpenBSD port to PA-RISC on HP 9000/700 systems was started by Michael Shalayeff around 1999. His porting efforts were based a lot on source code and information from the previous PA-RISC research projects Lites/HPPA and MkLinux. The first complete OpenBSD/hppa release was version 3.5, with PA-RISC having been supported since on most 32-bit workstation, some 64-bit workstations and some servers. An OpenBSD/hppa64 port to support PA-RISC 2.0 computers running natively in 64-bit mode was started in 2007, but never took off.

NetBSD/hppa is a free, open source Unix-like operating system, and supports PA-RISC computers since around 2005, called NetBSD/hp700 until the 7.0 release, as a Tier II port. The port focuses on 32-bit PA-RISC 1.1 computers and 64-bit PA-RISC 2.0 systems in 32-bit. The current effort is largely based on Michael Shalayeff’s work on the OpenBSD/hppa kernel from 2004 to 2005 and updated OpenBSD code later on.

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As soon as PA-RISC was released in the late 1980s, academic and industrial research projects started operating systems ports to PA-RISC. Several other operating systems have been ported to the PA-RISC platform over the time between the late 1980s and late 1990s. Most of them only reached development state and have long been unmaintained. Documentation is rare, some of it only in archives.

PA-RISC R&D operating systems timeline
Year HP Utah OSF Other
1988 HP Tut
1989 HP Tut HPBSD
1990 HP OSF/1 HPBSD Chorus (835)
1991 HP OSF/1 Mach 3/UX Chorus (720)
1993 HPBSD 2.0
1994 Mach 4/Lites MK-PA 6.0
1995 MK-PA 6.3
1996 Mach 4/Lites II MK-PA 7.x
1997 MkLinux

BSD: The premier among them was HPBSD from the University of Utah which was a port of 4.3BSD and later 4.4BSD to early 800s servers and specially the early 700s workstations. HPBSD contained commercial AT&T and HP code, and was never freely available.

Mach: Several ports of the Mach microkernel were undertaken during the early 1990s, with HP Tut using Mach 2.0 and the University of Utah trying Mach 3 and Mach 4. Porting efforts for OSF/1, the alliance Unix operating system from DEC, IBM, HP and others to compete with AT&T and Sun’s System V Unix, started around 1990. HP itself ported OSF/1 to PA-RISC, which was never widely available commercially. This port was superseded in the mid-1990s by the OSF RI Open Group Research Institute with several releases of MK-PA. All of the Mach ports were never really used widely as production systems, but formed the basis for other research projects and later the BSD and Linux ports.

Linux: Early Linux support on PA-RISC built upon the MkLinux research project from the mid-1990s by the Open Group/OSF, that ported a Linux kernel onto a Mach microkernel, which in turn built on the previous MK-PA OSF/1 port to PA-RISC.

Other: An internal HP research project was HP Tut from around 1988-89 to port HP-UX onto a Mach microkernel. The project apparently never suceeded far and moved on to merging parts of Mach 2.0 under HP-UX 2.0 to get something close to resembling Mach on PA-RISC. HP Tut was the basis for various other porting efforts and PA-RISC research projects within and outside of HP.

Another micro-kernel operating system was Chorus by INRIA with a development port to PA-RISC done in 1990-1991 at the Oregon Graduate Institute (OGI) for the HP 9000/834 system, based on based on Chorus v3.3/MiX v3.2. Hardware support and functionality was limited, with apparently no network interfaces or disk devices supported and console I/O depending on PDC and IODC routines. Code from various earlier projects was used, including from HP-UX 2.0 and HP Tut, HP-UX on 2.0 Mach. A later project ported Chorus v3.4 to the 9000/720 workstation a popular target for OS/Unix porting efforts at that time.

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The approximate timeline of PA-RISC operating system development begins in 1988 as follows.

PA-RISC operating systems timeline, - full support, - partial support
Year HP-UX Linux OpenBSD NetBSD HP-BSD Mach 3 Mach 4 OSF/1 MkLinux NeXTSTEP
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2021 █ █

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Further reading