PA-RISC
| Designer | Hewlett-Packard |
|---|---|
| Bits | 64-bit (32→64) |
| Introduced | 1986 (1996 PA-RISC 2.0) |
| Version | 2.0 (1996) |
| Design | RISC |
| Encoding | Fixed |
| Branching | Compare and branch |
| Endianness | Big |
| Extensions | Multimedia Acceleration eXtensions (MAX), MAX-2 |
| Open | No |
| Registers | |
| General purpose | 32 |
| Floating point | 32 64-bit (16 64-bit in PA-RISC 1.0) |
PA-RISC is an instruction set architecture (ISA) developed by Hewlett-Packard. As the name implies, it is a reduced instruction set computer (RISC) architecture, where the PA stands for Precision Architecture. The design is also referred to as HP/PA for Hewlett Packard Precision Architecture.
The architecture was introduced on 26 February 1986, when the HP 3000 Series 930 and HP 9000 Model 840 computers were launched featuring the first implementation, the TS1.
PA-RISC has been succeeded by the Itanium (originally IA-64) ISA, jointly developed by HP and Intel. HP stopped selling PA-RISC-based HP 9000 systems at the end of 2008 but supported servers running PA-RISC chips until 2013.
In the late 1980s, HP was building four series of computers, all based on CISC CPUs. One line was the IBM PC compatible Intel i286-based Vectra Series, started in 1986. All others were non-Intel systems. One of them was the HP Series 300 of Motorola 68000-based workstations, another Series 200 line of technical workstations based on a custom silicon on sapphire (SOS) chip design, the SOS based 16-bit HP 3000 classic series, and finally the HP 9000 Series 500 minicomputers, based on their own (16 and 32-bit) FOCUS microprocessor. HP planned to use PA-RISC to move all of their non-PC compatible machines to a single RISC CPU family.
Precision Architecture was introduced in 1986. It had thirty-two 32-bit integer registers and sixteen 64-bit floating-point registers. The number of floating-point registers was doubled in the 1.1 version to 32 once it became apparent that 16 were inadequate and restricted performance. The architects included Allen Baum, Hans Jeans, Michael J. Mahon, Ruby Bei-Loh Lee, Russel Kao, Steve Muchnick, Terrence C. Miller, David Fotland, and William S. Worley.
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