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ARM, originally Acorn RISC Machine, is a family of reduced instruction set computing (RISC) architectures for computer processors, configured for various environments, developed by British company ARM Holdings. A RISC-based computer design approach means ARM processors require significantly fewer transistors than typical complex instruction set computing (CISC) x86 processors in most personal computers. This approach reduces costs, heat and power use. Such reductions are desirable traits for light, portable, battery-powered devicesincluding smartphones, laptops, tablet and notepad computers, and other embedded systems. A simpler design facilitates more efficient multi-core CPUs and higher core counts at lower cost, providing improved energy efficiency for servers.〔("Some facts about the Acorn RISC Machine" ) Roger Wilson posting to comp.arch, 2 November 1988. Retrieved 25 May 2007.〕〔("ARM Cores Climb Into 3G Territory" ) by Mark Hachman, 2002.〕〔("The Two Percent Solution" ) by Jim Turley 2002.〕 ARM Holdings develops the instruction set and architecture for ARM-based products, but does not manufacture products. The company periodically releases updates to its cores. All cores from ARM Holdings support a 32-bit address space (only pre-ARMv3 chips, as in original Acorn Archimedes, had smaller) and 32-bit arithmetic; the ARMv8-A architecture, announced in October 2011, adds support for a 64-bit address space and 64-bit arithmetic. Instructions for ARM Holdings' cores have 32 bits wide fixed-length instructions, but later versions of the architecture also support a variable-length instruction set that provides both 32- and 16-bit wide instructions for improved code density. Some cores can also provide hardware execution of Java bytecodes. ARM Holdings licenses the chip designs and the ARM instruction set architectures to third parties, who design their own products that implement one of those architecturesincluding systems-on-chips (SoC) that incorporate memory, interfaces, radios, etc. Currently, the widely used Cortex cores, older "classic" cores, and specialized SecurCore cores variants are available for each of these to include or exclude optional capabilities. Companies that make chips that implement an ARM architecture include Analog Devices, Apple, AppliedMicro, Atmel, Broadcom, Cypress Semiconductor, Freescale Semiconductor, Nvidia, NXP, Qualcomm, Renesas, Samsung Electronics, ST Microelectronics and Texas Instruments. Qualcomm introduced new three-layer 3D chip stacking in their 2014–15 ARM SoCs such as in their first 20 nm 64-bit octa-core. Globally ARM is the most widely used instruction set architecture in terms of quantity produced. The low power consumption of ARM processors has made them very popular: over 50 billion ARM processors have been produced , of which 10 billion were produced in 2013〔(【引用サイトリンク】title=ARM 50 Billion Chips )〕 and "ARM-based chips are found in nearly 60 percent of the world’s mobile devices". The ARM architecture (32-bit) is the most widely used architecture in mobile devices, and most popular 32-bit one in embedded systems.〔 In 2005, about 98% of all mobile phones sold used at least one ARM processor. According to ARM Holdings, in 2010 alone, producers of chips based on ARM architectures reported shipments of 6.1 billion ARM-based processors, representing 95% of smartphones, 35% of digital televisions and set-top boxes and 10% of mobile computers. ==History== The British computer manufacturer Acorn Computers first developed the Acorn RISC Machine architecture (ARM) in the 1980s to use in its personal computers. Its first ARM-based products were coprocessor modules for the BBC Micro series of computers. After the successful BBC Micro computer, Acorn Computers considered how to move on from the relatively simple MOS Technology 6502 processor to address business markets like the one that was soon dominated by the IBM PC, launched in 1981. The ''Acorn Business Computer'' (ABC) plan required that a number of second processors be made to work with the BBC Micro platform, but processors such as the Motorola 68000 and National Semiconductor 32016 were considered unsuitable, and the 6502 was not powerful enough for a graphics based user interface. According to Sophie Wilson, all the tested processors at that time performed about the same, with about a 4 Mbit/second bandwidth. After testing all available processors and finding them lacking, Acorn decided it needed a new architecture. Inspired by white papers on the Berkeley RISC project, Acorn considered designing its own processor. A visit to the Western Design Center in Phoenix, where the 6502 was being updated by what was effectively a single-person company, showed Acorn engineers Steve Furber and Sophie Wilson they did not need massive resources and state-of-the-art research and development facilities. Wilson developed the instruction set, writing a simulation of the processor in BBC BASIC that ran on a BBC Micro with a second 6502 processor. This convinced Acorn engineers they were on the right track. Wilson approached Acorn's CEO, Hermann Hauser, and requested more resources. Once she had approval, he assembled a small team to implement Wilson's model in hardware. 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「ARM architecture」の詳細全文を読む スポンサード リンク
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