ARM, originally Acorn Risc Machine, is a family of reduced instruction set computing (RISC) instruction set 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 devices—?including 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.
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 bits 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 architectures—?including 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 as of 2014, of which 10 billion were produced in 2013 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.