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. History 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. The Precision Architecture is the result of what was known inside Hewlett-Packard as the Spectrum program. HP planned to use Spectrum to move all of their non-PC compatible machines to a single RISC CPU family. Work began on the Precision Architecture at HP Laboratories in early 1982 defining the instruction set and virtual memory system, and the first TTL implementation began in April 1983, with simulation of the processor occurring in 1983, and with a complete processor delivered to software developers in July 1984. Systems prototyping followed, with "lab prototypes" being produced in 1985 and product prototypes in 1986. The first processors were introduced in products during 1986. It has 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. The first implementation was the TS1, a central processing unit built from discrete transistor–transistor logic (74F TTL) devices. Later implementations were multi-chip VLSI designs fabricated in NMOS processes (NS1 and NS2) and CMOS (CS1