Early PA-RISC Systems

The first PA-RISC systems were released in the 1980s in the HP 9000/800 Series, which were all server systems (although some had graphics capabilities). Both the technical (PA-RISC was new) and marketing landscape was rather fluid then in the 1980s, as HP had almost dozens of other product categories that it was selling, and RISC and Unix servers were rather a niche.

Thus, information on these very early models and their details could be rather inconsistent, to say the least. This includes HP documentation (both sales and technical), which not always describe the architecture of these early systems very coherently. Much of the information here was pieced together from old news articles and press releases, plus the documentation available at the HP Computer Museum.

First PA-RISC Server, TS-1 (TTL)

The first commercial PA-RISC product appeared in 1986 with the HP 9000/840 (Indigo) computer, based on a six-board TTL implementation of the 32-bit PA-RISC 1.0 architecture, TS-1, running at 8 MHz. The TTL boards measure 8.4×11.3″, SRAMs/PALs and about 150 ICs each. The TS-1 boards implement the processor pipeline, a 4096-entry TLB and 128  KB (L1) cache, divided into 64  KB for each data and instruction.2

Two main buses are used in the I/O system:

  1. Central Bus (CTB — also called MidBus) connects the processor to the main memory and the secondary I/O bus (see below). CTB is 32-bit wide and has a clock speed of 8 MHz, with a sustained transfer rate of 20 MB/s. Seven slots for general purpose I/O cards are available.
  2. Channel I/O (CIO) is the central device I/O bus. Up to three CIO buses (also called CIBs) are supported in a single 9000/840 computer. (Others mention only one CIO channel on the 9000/840 — all three channels apparently were reserved for the very similar HP 3000/930.) CIO/CIB is 16-bit wide and achieves a transfer rate of 5 MB/s with a clock speed of 4 MHz. Seven (shared) I/O slots are available. Supported devices on CIO include HP-IB (Hewlett-Packard Interface-Bus, commonly used for instrumentation and measurement devices) and networking adapters.

Seven shared slots for I/O and memory are available, for up to 112 MB of RAM (7×16 MB; 2-16 MB memory modules were supported). The optional graphics adapter used one I/O and one memory slot, reducing the maximum RAM to 96 MB. Included by default into the system is a separate Floating Point Coprocessor (FPC) board. The 840 could be upgraded via a CPU board swap to 825, 835 or 845s retaining the case and memory and I/O boards.

It achieved about 4.5 MIPS and ran HP-UX version 1.0 (heavily BSD-based) up until version 10.01 (the pre-Y2k release). Storage and media devices were attached to the HP-IB bus, SCSI was only later (and with newer boot ROMs) available.

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Between 1987 and 1988, first systems with 32-bit PA-RISC 1.0 processors implemented in NMOS-III logic, the PA-RISC NS-1, appeared:3

HP 9000/825 FireFox (also HP 9000/825S):

HP 9000/835 TopGun (also HP 9000/835S):

HP 9000/850 Cheetah (also HP 9000/850S):

RAM could be expanded with 16 MB memory arrays, i.e., memory boards.

The systems use three main buses, expanding the original 9000/840 architecture:4

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Later, in 1989, similar computers based on the NS-2, a revamped NS-1, appeared (from early 1989 till late 1990). The later PA-RISC 1.0 and CIO bus based servers include:5

HP 9000/845 ShoGun:

HP 9000/855 Jaguar (also HP 9000/855S):

HP 9000/860 (also HP 9000/860S) Cougar:

These systems are all based on the same I/O architecture and CIO devices and faciliate the same CPU design — PA-RISC 1.0 NS-2. The 860 could be upgraded with newer CPU boards to a 865 or 870 (see below).

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Low-Cost NS-2

Lower-end and more compact servers were introduced between 1989 and 1990, based on the NS-2 and PCX processors but already using the HP-PB I/O bus:7

HP 9000/822 SilverFox Low:

HP 9000/832 SilverFox High:


The HP 9000/842, 9000/852, 9000/865 and the multi-processor 9000/870 (the first PA-RISC SMP system) include the first PA-RISC processors implemented in CMOS — the PA-RISC 1.0 PCX. These systems are very similar to the NS-2 based servers (with the 860 being board-upgradeable to a 865 or 870) and feature the same principal system and I/O architecture (with a slightly modified CPU/SPU architecture).6 These system use the same 16 MB memory arrays as earlier servers but could additionally use 64 MB boards.

HP 9000/842 SilverBullet Low:

HP 9000/852 SilverBullet High:

HP 9000/865 Panther:

HP 9000/870 Panther (also HP 9000/870S):

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Low-Cost PCX

Lower-end and more compact servers were introduced around 1990, based on the NS-2 and PCX processors but already using the HP-PB I/O bus. The 9000/808 and 9000/815 were entry-level serves, based on the first PA-RISC processor implemented in CMOS — the PA-RISC 1.0 PCX; introduced in 1989.

HP 9000/808:

HP 9000/815:

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Assorted MIPS benchmark numbers for systems with known, unambigious results, in ascending order.

Model MIPS
840 4.5
825 9
822 10
850 14
835 14
832 15
845 22
855 22
842 30
852 50

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  1. INFORMATION ON HP9000 SERVERS AND WORKSTATIONS Hewlett Packard Company (1999. Accessed January 2007) and The HP 3000/HP 9000 model spreadsheet (Excel spreadsheet) Allegro Consultants (2004. Accessed January 2007)
  2. Wayne E. Holt (ed.), Beyond RISC! An Essential Guide to Hewlett-Packard Precision Architecture, p. 95-102. (January 1988: Software Research Northwest Inc.) and Hardware Design of the First HP Precision Architecture Computers (PDF) David A. Fotland et al (March 1987: Hewlett-Packard Journal)
  3. HP 3000 Series 950 and HP 9000 Model 850S Family CE Handbook (PDF) Hewlett-Packard Company (October 1990. Accessed January 2008 at and HP 9000 Series 800 Model 825S Hardware Technical Data (PDF) Hewlett-Packard Company (September 1988. Accessed January 2008 at and HP 3000/925 and HP 9000/825/835 Computer Systems CE Handbook (PDF) Hewlett-Packard Company (May 1988. Accessed January 2008 at and New midrange members of the Hewlett-Packard Precision Architecture Computer Family Thomas O. Meyer et al (June 1989: Hewlett Packard Journal. Accessed January 2008 at
  4. Wayne E. Holt, Beyond RISC!
  5. Hewlett-Packard Company, HP 3000 Series 950 and HP 9000 Model 850S Family CE Handbook
  6. Ibid.
  7. HP 9000 Series 800 Model 822S/832S Technical Data (PDF) Hewlett-Packard Company (1989. Accessed January 2008 at
  8. For HP 9000/840: Interview with David Fotland, September/October 2008

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