| Version |
ARMv6, ARMv5, ARMv4T, ARMv3, ARMv2 |
| Encoding |
32-bit except Thumb extension uses mixed 16- and 32-bit instructions. |
| Endianness |
Bi (Little as default) in ARMv3 and above |
| Extensions |
Thumb, Jazelle |
| Registers |
| General purpose |
16x 32-bit integer registers including PC (26-bit addressing in older) and SP |
ARM is a family of instruction set architectures for computer processors based on a reduced instruction set computing (RISC) architecture developed by British company ARM Holdings.
A RISC-based computer design approach means ARM processors require significantly fewer transistors than typical processors in average computers. This approach reduces costs, heat and power use. These 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 higher processing power and improved energy efficiency for servers and supercomputers.[3][4][5]
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. Current cores from ARM Holdings support a 32-bitaddress space and 32-bit arithmetic; the recently introduced ARMv8-A architecture adds support for a 64-bit address space and 64-bit arithmetic. Instructions for ARM Holdings' cores have 32-bit-wide fixed-length instructions, but later versions of the architecture also support a variable-length instruction set that provides both 32-bit 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 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 produce ARM products include Apple, Nvidia, Qualcomm, Rockchip, Samsung Electronics, and Texas Instruments. Apple first implemented the ARMv8-A architecture in the Apple A7 chip in the iPhone 5S.
In 2005, about 98% of all mobile phones sold used at least one ARM processor.[6] The low power consumption of ARM processors has made them very popular: 37 billion ARM processors have been produced as of 2013[update], up from 10 billion in 2008.[7] The ARM architecture (32-bit) is the most widely used architecture in mobile devices, and most popular 32-bit one in embedded systems.[8]
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. It is the most widely used 32-bit instruction set architecture in terms of quantity produced.[9][10]