thumb|IBM PowerPC 601 microprocessor
PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple–IBM–Motorola alliance, known as AIM. PowerPC, as an evolving instruction set, has been named Power ISA since 2006, while the old name lives on as a trademark for some implementations of Power Architecture–based processors.
Originally intended for personal computers, the architecture is well known for being used by Apple's desktop and laptop lines from 1994 until 2006, and in several videogame consoles including Microsoft's Xbox 360, Sony's PlayStation 3, and Nintendo's GameCube, Wii, and Wii U. PowerPC was also used for the Curiosity and Perseverance rovers on Mars and a variety of satellites. It has since become a niche architecture for personal computers, particularly with AmigaOS 4 implementations, but remains popular for embedded systems.
PowerPC was the cornerstone of AIM's PReP and Common Hardware Reference Platform (CHRP) initiatives in the 1990s. It is largely based on the earlier IBM POWER architecture, and retains a high level of compatibility with it; the architectures have remained close enough that the same programs and operating systems will run on both if some care is taken in preparation. Newer chips in the Power series use the Power ISA.
History
The history of RISC began with IBM's 801 research project, on which John Cocke was the lead developer, where he developed the concepts of RISC in 1975–78. 801-based microprocessors were used in a number of IBM embedded products, eventually becoming the 16-register IBM ROMP processor used in the IBM RT PC. The RT PC was a rapid design implementing the RISC architecture. Between the years of 1982 and 1984, IBM started a project to build the fastest microprocessor on the market; this new 32-bit architecture became referred to as the America Project throughout its development cycle, which lasted for approximately 5–6 years. The result is the POWER instruction set architecture, introduced with the RISC System/6000 in early 1990.
The original POWER microprocessor, one of the first superscalar RISC implementations, is a high performance, multi-chip design. IBM soon realized that a single-chip microprocessor was needed in order to scale its RS/6000 line from lower-end to high-end machines. Work began on a one-chip POWER microprocessor, designated the RSC (RISC Single Chip). In early 1991, IBM realized its design could potentially become a high-volume microprocessor used across the industry.
Apple and Motorola involvement
Apple had already realized the limitations and risks of its dependency upon a single CPU vendor at a time when Motorola was falling behind on delivering the 68040 CPU. Furthermore, Apple had conducted its own research and made an experimental quad-core CPU design called Aquarius, asked Motorola to join the discussions due to their long relationship, Motorola having had more extensive experience with manufacturing high-volume microprocessors than IBM, and to form a second source for the microprocessors. This three-way collaboration between Apple, IBM, and Motorola became known as the AIM alliance.
In 1991, the PowerPC was just one facet of a larger alliance among these three companies. At the time, most of the personal computer industry was shipping systems based on the Intel 80386 and 80486 chips, which have a complex instruction set computer (CISC) architecture, and development of the Pentium processor was well underway. The PowerPC chip was one of several joint ventures involving the three alliance members, in their efforts to counter the growing Microsoft-Intel dominance of personal computing.
For Motorola, POWER looked like an unbelievable deal. It allowed the company to sell a widely tested and powerful RISC CPU for little design cash on its own part. It also maintained ties with an important customer, Apple, and seemed to offer the possibility of adding IBM too, which might buy smaller versions from Motorola instead of making its own.
At this point Motorola already had its own RISC design in the form of the 88000, which was doing poorly in the market. Motorola was doing well with its 68000 family and the majority of the funding was focused on this. The 88000 effort was somewhat starved for resources.
The 88000 was already in production, however; Data General was shipping 88000 machines and Apple already had 88000 prototype machines running. The 88000 had also achieved a number of embedded design wins in telecom applications. If the new POWER one-chip version could be made bus-compatible at a hardware level with the 88000, that would allow both Apple and Motorola to bring machines to market far faster since they would not have to redesign their board architecture.
The result of these various requirements is the PowerPC (performance computing) specification. The differences between the earlier POWER instruction set and that of PowerPC is outlined in Appendix E of the manual for PowerPC ISA v.2.02.
When the first PowerPC products reached the market, they were met with enthusiasm. In addition to Apple, both IBM and the Motorola Computer Group offered systems built around the processors. Microsoft released Windows NT 3.51 for the architecture, which was used in Motorola's PowerPC servers, and Sun Microsystems offered a version of its Solaris OS. IBM ported its AIX Unix. Workplace OS featured a new port of OS/2 (with Intel emulation for application compatibility), pending a successful launch of the PowerPC 620. Throughout the mid-1990s, PowerPC processors achieved benchmark test scores that matched or exceeded those of the fastest x86 CPUs.
Ultimately, demand for the new architecture on the desktop never truly materialized. Windows, OS/2, and Sun customers, faced with the lack of application software for the PowerPC, almost universally ignored the chip. IBM's Workplace OS platform (and thus, OS/2 for PowerPC) was summarily canceled upon its first developers' release in December 1995 due to the simultaneous buggy launch of the PowerPC 620. The PowerPC versions of Solaris and Windows were discontinued after only a brief period on the market. Only on the Macintosh, due to Apple's persistence, did the PowerPC gain traction. To Apple, the performance of the PowerPC was a bright spot in the face of increased competition from Windows 95 and Windows NT-based PCs.
With the cancellation of Workplace OS, the general PowerPC platform (especially AIM's Common Hardware Reference Platform) was instead seen as a hardware-only compromise to run many operating systems one at a time upon a single unifying vendor-neutral hardware platform.