PA-RISC

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.

PA-RISC (HP/PA)

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)

HP PA-RISC 7300LC microprocessor

HP 9000 C110 PA-RISC workstation booting Debian GNU/Linux

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.[1][2]

PA-RISC has been succeeded by the Itanium (originally IA-64) ISA, jointly developed by HP and Intel.[3] HP stopped selling PA-RISC-based HP 9000 systems at the end of 2008 but supported servers running PA-RISC chips until 2013.[4]

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.

Precision Architecture is the result of what was known inside Hewlett-Packard as the Spectrum program.[5] HP planned to use Spectrum to move all of their non-PC compatible machines to a single RISC CPU family.

The first processors were 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.[6]

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 and PCX).[7] They were first used in a new series of HP 3000 machines in the late 1980s – the 930 and 950, commonly known at the time as Spectrum systems, the name given to them in the development labs. These machines ran MPE-XL. The HP 9000 machines were soon upgraded with the PA-RISC processor as well, running the HP-UX version of UNIX.

Other operating systems ported to the PA-RISC architecture include Linux, OpenBSD, NetBSD and NeXTSTEP.

An interesting aspect of the PA-RISC line is that most of its generations have no Level 2 cache. Instead large Level 1 caches are used, formerly as separate chips connected by a bus, and now integrated on-chip. Only the PA-7100LC and PA-7300LC had L2 caches. Another innovation of the PA-RISC was the addition of vectorized instructions (SIMD) in the form of MAX, which were first introduced on the PA-7100LC.

Precision RISC Organization, an industry group led by HP, was founded in 1992, to promote the PA-RISC architecture. Members included Convex, Hitachi, Hughes Aircraft, Mitsubishi, NEC, OKI, Prime, Stratus, Yokogawa, Red Brick Software, and Allegro Consultants, Inc..

The ISA was extended in 1996 to 64 bits, with this revision named PA-RISC 2.0. PA-RISC 2.0 also added fused multiply–add instructions, which help certain floating-point intensive algorithms, and the MAX-2 SIMD extension, which provides instructions for accelerating multimedia applications. The first PA-RISC 2.0 implementation was the PA-8000, which was introduced in January 1996.

CPU specifications

Model	Marketing name	Year	Frequency [MHz]	Memory Bus [MB/s]	Process [μm]	Transistors [millions]	Die size [mm²]	Power [W]	Dcache [kB]	Icache [kB]	L2 cache [MB]	ISA	Notes
TS-1	?	1986	8	?	?	—	—	?	?	?	—	1.0
CS-1	?	1987	8	?	1.6	0.164	72.93	1	—	0.25	—	1.0	[8]
NS-1	?	1987	25/30	?	1.5	0.144	70.56	?	?	?	—	1.0	[9]
NS-2	?	1989	27.5/30	?	1.5	0.183	196	27	512	512	—	1.0	[10]
PCX	?	1990	?	?	?	?	?	?	?	?	?	1.0
PCX-S	PA-7000	1991	66	?	1.0	0.58	201.6	?	256	256	—	1.1a
PCX-T	PA-7100	1992	33–100	?	0.8	0.85	196	?	2048	1024	—	1.1b
PCX-T	PA-7150	1994	125	?	0.8	0.85	196	?	2048	1024	—	1.1b
PCX-T'	PA-7200	1994	120	960	0.55	1.26	210	30	1024	2048	—	1.1c
PCX-L	PA-7100LC	1994	60–100	?	0.75	0.9	201.6	7–11	—	1	2	1.1d
PCX-L2	PA-7300LC	1996	132–180	?	0.5	9.2	260.1	?	64	64	0–8	1.1e
PCX-U	PA-8000	1996	160–180	960	0.5	3.8	337.68	?	1024	1024	—	2.0
PCX-U+	PA-8200	1997	200–240	960	0.5	3.8	337.68	?	2048	2048	—	2.0
PCX-W	PA-8500	1998	300–440	1920	0.25	140	467	?	1024	512	—	2.0	[11]
PCX-W+	PA-8600	2000	360–550	1920	0.25	140	467	?	1024	512	—	2.0	[11]
PCX-W2	PA-8700(+)	2001	625–875	1920	0.18	186	304	<7.1@1.5 V	1536	768	—	2.0
Mako	PA-8800	2003	800–1000	6400	0.13	300	361	?	768/core	768/core	0 or 32	2.0
Shortfin	PA-8900	2005	800–1100	6400	0.13	?	?	?	768/core	768/core	0 or 64	2.0

See also

• Hombre chipset – A PA-7150-based chipset with a complete multimedia system for Commodore-Amiga

References

1. "One Year Ago". (26 February 1987). Computer Business Review.
2. Rosenbladt, Peter (September 1987). "In this Issue" (PDF). Hewlett-Packard Journal. 38 (9): 3. ... In the March 1987 issue we described the HP 3000 Series 930 and HP 9000 Model 840 Computers, which were HP's first realizations of HP Precision Architecture in off-the-shelf TTL technology. ...
3. HP Completes Its PA-RISC Road Map With Final Processor Upgrade
4. How long will HP continue to support HP 9000 systems?
5. Worley, William S. (August 1986). "Hewlett-Packard Precision Architecture: The Processor" (PDF). Hewlett-Packard Journal. 37 (8): 4–22. The HP Precision Architecture development program, known within HP as the Spectrum program, ...
6. Smotherman, Mark (2 July 2009). Recent Processor Architects.
7. Paul Weissmann. "Early PA-RISC Systems".
8. Marston, A.; et al. (1987). "A 32b CMOS single-chip RISC type processor". 1987 IEEE International Solid-State Circuits Conference. Digest of Technical Papers. pp. 28–29. doi:10.1109/ISSCC.1987.1157145.
9. Yetter, J.; et al. (1987). "A 15 MIPS 32b Microprocessor". ISSCC 1987. pp. 26–27. doi:10.1109/ISSCC.1987.1157220.
10. Boschma, Brian D.; et al. (1989). "A 30 MIPS VLSI CPU". IEEE International Solid-State Circuits Conference, 1989 ISSCC. Digest of Technical Papers. pp. 82–83, 299. doi:10.1109/ISSCC.1989.48191.
11. "HP L1000 & L2000 (rp5400/rp5450) Servers", openpa.net

External links

• LostCircuits Hewlett Packard PA8800 RISC Processor overview
• HP's documentation – page down for PA-RISC, architecture PDFs available
• OpenPA.net Comprehensive PA-RISC chip and computer information
• chipdb.org Images of different PA-RISC processors