What is ARM processor? - Definition from WhatIs.com
Part of the Microprocessors glossary:

An ARM processor is one of a family of CPUs based on the RISC (reduced instruction set computer) architecture developed by Advanced RISC Machines (ARM).

ARM makes 32-bit and 64-bit RISC multi-core processors. RISC processors are designed to perform a smaller number of types of computer instructions so that they can operate at a higher speed, performing more millions of instructions per second (MIPS).  By stripping out unneeded instructions and optimizing pathways, RISC processors provide outstanding performance at a fraction of the power demand of CISC (complex instruction set computing) devices.

ARM processors are extensively used in consumer electronic devices such as smartphones, tablets, multimedia players and other mobile devices, such as wearables. Because of their reduced instruction set, they require fewer transistors, which enables a smaller die size for the integrated circuitry (IC). The ARM processor’s smaller size, reduced complexity and lower power consumption makes them suitable for increasingly miniaturized devices.

ARM processor features include:

  • Load/store architecture.
  • An orthogonal instruction set.
  • Mostly single-cycle execution.
  • Enhanced power-saving design.
  • 64 and 32-bit execution states for scalable high performance.
  • Hardware virtualization support.

The simplified design of ARM processors enables more efficient multi-core processing and easier coding for developers. While they don't have the same raw compute throughput as the products of x86 market leader Intel, ARM processors sometimes exceed the performance of Intel processors for applications that exist on both architectures.

The head-to-head competition between the vendors is increasing as ARM is finding its way into full size notebooks.  Microsoft, for example, offers ARM-based versions of Surface computers. The cleaner code base of Windows RT versus x86 versions may be also partially responsible -- Windows RT is more streamlined because it doesn’t have to support a number of legacy hardwares.

ARM is also moving into the server market,  a move that represents a large change in direction and a hedging of bets on performance-per-watt over raw compute power. AMD offers 8-core versions of ARM processors for its Opteron series of processors. ARM servers represent an important shift in server-based computing. A traditional x86-class server with 12, 16, 24 or more cores increases performance by scaling up the speed and sophistication of each processor, using brute force speed and power to handle demanding computing workloads.

In comparison, an ARM server uses perhaps hundreds of smaller, less sophisticated, low-power processors that share processing tasks among that large number instead of just a few higher-capacity processors. This approach is sometimes referred to as “scaling out,” in contrast with the “scaling up” of x86-based servers.

The ARM architecture was originally developed by Acorn Computers in the 1980s.

See an introductory lecture on ARM processors:


This was last updated in January 2015
Contributor(s): Matthew Haughn, Stephen J. Bigelow
Posted by: Margaret Rouse

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