ARM Architecture

The ARM architecture (previously, the Advanced RISC Machine, and prior to that Acorn RISC Machine) is a 32-bit RISC processor architecture developed by ARM Limited that is widely used in a number of embedded designs. Because of their power saving features, ARM CPUs are dominant in the mobile electronics market, where low power consumption is a critical design goal.

Today, the ARM family accounts for approximately 75% of all embedded 32-bit RISC CPUs, making it one of the most prolific 32-bit architectures in the world. ARM CPUs are found in all corners of consumer electronics, from portable devices (PDAs, mobile phones, media players, handheld gaming units, and calculators) to computer peripherals (hard drives, desktop routers).

The ARM architecture includes the following RISC features :

• Load/store architecture

• No support for misaligned memory accesses (now supported in ARMv6 cores)

• Orthogonal instruction set

• Large 16 × 32-bit register file

• Fixed instruction width of 32 bits to ease decoding and pipelining, at the cost of decreased code density

• Mostly single-cycle execution

ARM licensees

ARM Ltd does not manufacture and sell CPU devices based on their own designs, but rather, licenses the processor architecture to interested parties. ARM offers a variety of licensing terms, varying in cost and deliverables.

To all licensees, ARM provides an integratable hardware description of the ARM core, as well as complete software development toolset (compiler, debugger, SDK), and the right to sell manufactured silicon containing the ARM CPU.

Today, the ARM family accounts for approximately 75% of all embedded 32-bit RISC CPUs, making it one of the most prolific 32-bit architectures in the world.

ARM's 2006 annual report and accounts state that royalties totaling $164.1 million were the result of licensees shipping 2.45 billion units. This is equivalent to 6.7 cents per unit shipped.

In the same year ARM's licensing revenues for processor cores were $119.5 million, in a year when 65 processor licenses were signed, an average of $1.84 million per license.

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