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ARM architecture refers to an instruction set architecture (ISA) that United Kingdom-based semiconductor manufacturer ARM Holdings, plc. develops. The technology is best known for its application on processors, or central processing units (CPUs), with low power consumption, or great energy efficiency. Also, it is designed with the concept of reduced instruction set computing (RISC), which means that it strives to optimize processor performance by simplifying instructions for faster execution. ARM-based CPUs in particular rely on a single-cycle execution.
English computer company Acorn Computers originated the ARM architecture in October 1983 when it started the Acorn RISC Machine project to come up with a more advanced processor for its business-oriented personal computers (PCs). This is mainly because the MOS Technology 6502, an 8-bit processor popular for its comparatively low cost, was too weak to handle certain computer features such as a graphics-based user interface.
The Acorn Archimedes, released in 1987, was the first computer to feature an ARM-based CPU. The second iteration, ARM2, is notable for outperforming the Intel 80286, or iAPX 286. This was a processor from fellow semiconductor company Intel Corp. and used on the IBM Personal Computer AT (IBM PC/AT) from International Business Machines. The success of the ARM-based processors led to the morphing of the company to Advanced RISC Machines Ltd. in 1990, then ARM Holdings by 1998.
ARM architecture comprises an orthogonal instruction set. Although the term orthogonal is used for something composed of right angles, in computer terminology, it is used to refer to a data object—in this case, an ISA—that functions without affecting others, or is statistically independent. The ARM architecture uses 32 bits, which is the maximum data size that it accommodates. More specifically, each processor using the instruction set has 16 32-bit registers, which are tiny storage units that provide high-speed access to data instead of allowing the CPU to get it from somewhere else at a slower rate.
Ironically, ARM architecture was initially designed for PCs. Instead, the x86 instruction set, which traces its origins to Intel’s 8086, or iAPX86, dominated the market by the end of the 1990s. Thus, IBM PC-compatible computers, as well as Macintosh computers from Apple, have x86 CPUs from companies such as Intel and Advanced Micro Devices (AMD).
Meanwhile, ARM shifted to smaller electronic devices, which are ideal for the technology’s simplified executions and low power consumption. By 2009, more than 90 percent of all mobile phones contained an ARM-based processor. Other devices that use ARM architecture for their CPUs include personal digital assistants (PDAs), portable multimedia players and calculators.