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:''Not to be confused with IBM PC or its clones.'' PowerPC (an acronym for Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a RISC instruction set architecture created by the 1991 Apple–IBM–Motorola alliance, known as ''AIM''. PowerPC, as an evolving instruction set, has since 2006 been named Power ISA, while the old name naturally lives on, as a legacy trademark for some implementations of Power Architecture based processors, and in software package identifiers. Originally intended for personal computers, PowerPC CPUs have since become popular as embedded and high-performance processors. PowerPC was the cornerstone of AIM's PReP and Common Hardware Reference Platform initiatives in the 1990s and while the architecture is well known for being used by Apple's Power Macintosh, PowerBook, iMac, iBook, and Xserve lines from 1994 to 2006 (before Apple's transition to Intel), its use in video game consoles and embedded applications provided an array of uses. In addition, PowerPC CPUs are still used in AmigaOne and third party AmigaOS 4 personal computers. PowerPC is largely based on IBM's earlier POWER instruction set 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 implement the full PowerPC instruction set. == 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 ROMP processor used in the IBM RT. The RT was a rapid design implementing the RISC architecture. Between the years of 1982-1984 IBM started a project to build the fastest microprocessor on the market; this new 64-bit architecture became referred to as the "America Project" throughout its development cycle which lasted for approximately 5–6 years. The result was 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, was 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 on a one-chip POWER microprocessor, designated the RSC (RISC Single Chip) began. In early 1991, IBM realized its design could potentially become a high-volume microprocessor used across the industry. IBM approached Apple with the goal of collaborating on the development of a family of single-chip microprocessors based on the POWER architecture. Soon after, Apple, being one of Motorola's largest customers of desktop-class microprocessors, asked Motorola to join the discussions due to their long relationship, its more extensive experience with manufacturing high-volume microprocessors than IBM, and to form a second source for the microprocessors. This three-way collaboration became known as AIM alliance, for Apple, IBM, Motorola. 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 had a CISC architecture, and development of the Pentium processor was well underway. The PowerPC chip was one of several joint ventures involving the three, in their efforts to counter the growing Microsoft-Intel dominance of personal computing. For Motorola, POWER looked like an unbelievable deal. It allowed them to sell a widely tested and powerful RISC CPU for little design cash on their own part. It also maintained ties with an important customer, Apple, and seemed to offer the possibility of adding IBM too, who 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 their 68000 family and the majority of the funding was focused on this. The 88000 effort was somewhat starved for resources. However, the 88000 was already in production; 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 was the PowerPC (''Performance Computing'') specification. The differences between the earlier POWER instruction set and PowerPC is outlined in Appendix E of the manual for PowerPC ISA v.2.02.〔(PowerPC User Instruction Set Architecture Book I, version 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 and planned a release of OS/2. 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. The PowerPC versions of Solaris, OS/2, 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. In parallel with the alliance between IBM and Motorola, both companies had development efforts underway internally. The PowerQUICC line was the result of this work inside Motorola. The 4xx series of embedded processors was underway inside IBM. The IBM embedded processor business grew to nearly 100 million dollars in revenue and attracted hundreds of customers. However, toward the close of the decade, manufacturing issues began plaguing the AIM alliance in much the same way they did Motorola, which consistently pushed back deployments of new processors for Apple and other vendors: first from Motorola in the 1990s with the G3 and G4 processors, and IBM with the 64-bit G5 processor in 2003. In 2004, Motorola exited the chip manufacturing business by spinning off its semiconductor business as an independent company called Freescale Semiconductor. Around the same time, IBM exited the 32-bit embedded processor market by selling its line of PowerPC products to Applied Micro Circuits Corporation (AMCC) and focusing on 64-bit chip designs, while maintaining its commitment of PowerPC CPUs toward game machine makers such as Nintendo's GameCube and Wii, Sony's PlayStation 3 and Microsoft's Xbox 360, of which the latter two both use 64-bit processors. In 2005 Apple announced they would no longer use PowerPC processors in their Apple Macintosh computers, favoring Intel-produced processors instead, citing the performance limitations of the chip for future personal computer hardware specifically related to heat generation and energy usage, as well as the inability of IBM to move the 970 (PowerPC G5) processor to the 3 GHz range. The IBM-Freescale alliance was replaced by an open standards body called Power.org. Power.org operates under the governance of the IEEE with IBM continuing to use and evolve the PowerPC processor on game consoles and Freescale Semiconductor focusing solely on embedded devices. IBM continues to develop PowerPC microprocessor cores for use in their application-specific integrated circuit (ASIC) offerings. Many high volume applications embed PowerPC cores. The PowerPC specification is now handled by Power.org where IBM, Freescale, and AMCC are members. PowerPC, Cell and POWER processors are now jointly marketed as the Power Architecture. Power.org released a unified ISA, combining POWER and PowerPC ISAs into the new Power ISA v.2.03 specification and a new reference platform for servers called PAPR (Power Architecture Platform Reference). , IBM's POWER microprocessors, which implement the Power ISA, are used by IBM in their IBM Power Systems, running IBM i, AIX, and Linux. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「PowerPC」の詳細全文を読む スポンサード リンク
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