Hardware Reference
In-Depth Information
cache. Because of the way power consumption is related to voltage and clock
speed, two CPUs on a chip consume far less power than one CPU at twice the
speed. As a consequence, the gain offered by Moore's law may be increasingly
exploited in the future to include more cores and larger on-chip caches, rather than
higher and higher clock speeds. Taking advantage of these multiprocessors poses
great challenges to programmers, because unlike the sophisticated uniprocessor
microarchitectures of the past that could extract more performance from existing
programs, multiprocessors require the programmer to explicitly orchestrate parallel
execution, using threads, semaphores, shared memory and other headache- and
bug-inducing technologies.
In the early 80s, the U.K.-based company Acorn Computer, flush with the suc-
cess of their 8-bit BBC Micro personal computer, began working on a second ma-
chine with the hope of competing with the recently released IBM PC. The BBC
Micro was based on the 8-bit 6502 processor, and Steve Furber and his colleagues
at Acorn felt that the 6502 did not have the muscle to compete with the IBM PC's
16-bit 8086 processor. They began looking at the options in the marketplace, and
decided that they were too limited.
Inspired by the Berkeley RISC project, in which a small team designed a
remarkably fast processor (which eventually led to the SPARC architecture), they
decided to build their own CPU for the project. They called their design the Acorn
RISC Machine (or ARM, which would later be rechristened the Advanced RISC
machine when ARM eventually split from Acorn). The design was completed in
1985. It included 32-bit instructions and data, and a 26-bit address space, and it
was manufactured by VLSI Technology.
The first ARM architecture (called the ARM2) appeared in the Acorn
Archimedes personal computer. The Archimedes was a very fast and inexpensive
machine for its day, running up to 2 MIPS (millions of instructions per second) and
costing only 899 British pounds at launch. The machine became very popular in
the UK, Ireland, Australia and New Zealand, especially in schools.
Based on the success of the Archimedes, Apple approached Acorn to develop
an ARM processor for their upcoming Apple Newton project, the first palmtop
computer. To better focus on the project, the ARM architecture team left Acorn to
create a new company called Advanced RISC Machines (ARM). Their new proc-
essor was called the ARM 610, which powered the Apple Newton when it was re-
lease in 1993. Unlike the original ARM design, this new ARM processor incorpor-
ated a 4-KB cache that significantly improved the design's performance. Although
the Apple Newton was not a great success, the ARM 610 did see other successful
applications including Acorn's RISC PC computer.
In the mid 1990s, ARM collaborated with Digital Equipment Corporation to
develop a high-speed, low-power version of the ARM, intended for energy-frugal
