Acorn RISC Machine
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ARM’s headquarters in Cambridge
The Acorn RISC Machine (or ARM) is a RISC processor architecture that is widely used in a number of applications. It is a very “pure” RISC implementation, and is considered one of the most elegant modern processors.
The ARM design was started in 1983 as a project at Acorn Computers Ltd. After being refused access to the upcoming Intel 80286 for newer generations of their computer line, they responded by starting up a team to design and build a new RISC based CPU, known as the Acorn RISC Machine.
The team, led by Roger Wilson and Steve Furber, started development of what in some ways represents an advanced MOS Technology 6502. Acorn had a long line of computers based on the 6502, so a chip that was similar to program could represent a significant advantage for the company.
The team completed development samples called ARM1 by 1985, and the first “real” production systems as ARM2 the following year. The ARM2 featured a 32-bit data bus and 24-bit address bus, with 16 registers. The ARM2 was possibly the simplest useful processor in the world, with only 30,000 transistors (compare with the four-year older Motorola 68000‘s 68,000). Much of this simplicity comes from not having microcode (which represents about 1/4 to 1/3rd of the 68000) and (like most CPU’s of the day) not including any cache. This simplicity leads to its excellent low-power needs, and yet it performed better than the 286.
In the late 1980s Apple Computer started working with Acorn on newer versions of the ARM core. The work was so important that Acorn spun off the design team in 1990 into a new company called Advanced RISC Machines. For this reason you often see ARM lengthened to Advanced RISC Machine instead of Acorn RISC Machine. Advanced RISC Machines became ARM Limited when the company floated on the London Stock Exchange and NASDAQ in 1998.
This work would eventually turn into the ARM6. The first models were released in 1991, and Apple used the ARM6-based ARM 610 as the basis for their Apple NewtonNewton was one of the world’s first personal digital assistants (PDA). Developed by Apple Computer and sold from 1993 to 1998, it was based on the ARM processor, and featured handwriting recognition. Apple’s official name for the device was MessagePad the PDA.
The core has remained largely the same size throughout these changes. ARM2 had 30,000 transistors, while the ARM6 grew to only 35,000. The idea is that the end-user combinesthe ARM core with a number of optional parts to produce a complete CPU, one that can be built on old fabA fab is a factory for producing integrated circuits. It is a short form of “fabrication”. Another term commonly used is semiconductor foundry . These companies gain their advantage by having access to specific manufacturing technologies, known in the inds and still deliver lots of performance at a low cost.
The most successful implementation has been the ARM7TDMI with hundreds of millions sold in cellular phones. While ARMs business has always been to sell IP-cores, some of the licenses generated microcontrollers based on this core.
DECDigital Equipment Corporation is a pioneering company in the American computer industry. They are generally referred to within the computing industry as DEC .
The DEC Alpha also known as the Alpha AXP is a 64-bit RISC microprocessor originally developed and fabricated by Digital Equipment Corp. (DEC), which used it in its own line of workstations and produced the StrongARM. At 233MHz this CPU drew only 1 watt of power (more recent versions draw far less).
This work was later passed to Intel as a part of a lawsuit settlement, and Intel took the opportunity to replace their ailing i860 and i960 designs with the StrongARM. Intel have since developed their own high performance implementation known by the name XScale. Motorola, IBM, Texas Instruments, Nintendo, Philips, VLSI, Atmel and Samsung have also licensed the basic ARM design for various uses. The ARM chip has become one of the most used CPU designs in the world, found in everything from hard drives, to mobile phones, to routers, to calculators. Today it accounts for over 75% of all 32-bit embedded CPU’s.