ARM ISA

General

History Families

Variants

26-bit 32-bit 64-bit

Extensions

ARM Thumb ThumbEE Jazelle VFP Neon Helium

Topics

Addressing Modes Registers Assembly Interrupts CPSR Modes Calling Convention Microarchitectures

Versions(all)

ARMv1 ARMv2 ARMv2a ARMv3 ARMv4 ARMv5 ARMv6 ARMv7 ARMv8 ARMv8.1 ARMv8.2 ARMv8.3

History of ARM:

BBC & ARM1

See also: ARM1

In 1980 BBC started the Computer Literacy Project. At the time BBC wanted the project to center around a microcomputer. BBC entered talks with a number of computer companies, among them was Acorn Computers. Early in 1980 Acorn released the Acorn Atom and by that time they were already working on their next project, Proton. Acorn got an early prototype working to demo BBC. The Proton met BBC's specification resulting in a contract signed in February of 1981. In December of 1981 Acorn Computers introduced the BBC Micro, becoming a great success.

The Acorn BBC Micro made use of the 6502, a highly popular 8-bit microprocessor operating at 2 MHz. The early 80s were transforming quickly and by January 1983 Apple introduced the Apple Lisa which utilized the Motorola 68000, a much more powerful 16-bit microprocessor operating at 5 MHz. The Lisa included many other cutting edge features such as a windowing environment.

ARM1 Evaluation System board

Recognizing the need for more powerful computers, Acorn formed the Advanced Research and Development division. In 1983 the group was established in an attempt to develop a their own RISC processor. The initial outcome of the project was the first ARM processor. Initially stood for Acorn RISC Machine, the name was later changed to Advanced RISC Machine.

Sophie Wilson and Steve Furber designed a reference model in BBC BASIC in just 808 lines of code. The first processor, the ARM1, was fabricated on VLSI Technology's 3 µm process using just 24,800 transistors. First silicon prototypes were delivered on April 26 1985.

The ARM1 had a few major bottlenecks - primarily the lack of hardware multiplication support resulted in considerable performance issues in related code. The problem was compounded by the fact that the ARM1 had no ability to support coprocessors which were needed for scientific applications that could make use of a powerful FPU coprocessor. By the following year Acorn reimplemented the ARM1 on a smaller process along with a number of enhancements designed to address those precise problems. The new design became the ARM2.

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