Lessons from Discarded Computer Architectures - History of Computing: Learning from the Past - page 200

consumption, and were ideal for mobile application where battery life matters. Lead-
ing into 2007 they were used in over 98% of the world's billion mobile phones [8].
A person who links the withered branch of the BBC computer to the highly suc-
cessful ARM processor tree is Tudor Brown. He studied Electrical Engineering at
Cambridge University, and was awarded an M.A. in Electrical Sciences. He was en-
ticed back to the city again in 1983 to join Acorn Computers, where he worked on the
ARM R&D program as Principal Engineer. When ARM spun out from Acorn as a
joint venture with Apple, he became Engineering Director and then Chief Technical
Officer from 1993 [27] In October 2000 he was appointed Executive Vice President,
Global Development and in October 2001, joined the board of ARM as Chief Operat-
ing Officer. He became President in 2008 with responsibility for developing high-
level relationships with industry partners and governmental agencies and for regional
development [9].
This withered branch of computer architecture contains the seeds of a comparison
between marketing success and intellectual striving. It embraces the success of algo-
rithmic thinking based upon uni-processor machines and a failure to make progress
with multi-processor computers. To explain the next withered branch, we need to give
an overview of the instruction sets associated with particular processor families.
3 Links between Processor Families and Operating Systems
An operating system is a collection of programming codes designed to provide a con-
sistent interface between hardware and the software applications run by the computer
user. In this sense, an operating system can run on any hardware to which it has been
adapted, and the software application will run as expected. When an operating system
runs consistently on more than one processor, it must be coded using a different in-
struction set for each. The instruction set consists of all the various instructions that
the processor can execute.
It can be quite difficult to create and maintain an operating system, and this causes
some inertia in the versioning process to cope with different processors. Therefore
while it is not strictly necessary for a particular operating system to be associated with
a specific processor development family, in the main this has been the case.
The two most significant such associations have been Windows with Intel x86 line
processors and Apple's Macintosh operating system with Motorola 6xxx line of proc-
essors and others. The Microsoft Disk Operating System (MS-DOS) with its succes-
sive versions of Microsoft Windows has been developed to run on 16, 32bit and 64bit
processors from Intel; currently the Atom and Core-i7. These have been developed
from the original 8086 (16bits, 1978), through the 80486 and Pentium (in 1993)
versions [10].
The Apple line of succession began in 1977 with the Apple II using the Motorola
6502 processor which ran operating systems such as CP/M [11]. The Apple II was the
first true “personal computer” which was factory built, inexpensive and easy to learn
and use. Provided with the most extensive set of software and low cost floppy disks,
the Apple II was also the first personal computer capable of color graphics and easy
modem operation. Development of the Visicalc spreadsheet program created a busi-
ness tool that made adoption of Apple II a regular part of business [12]. The processor