252
A UNIVERSAL
COMPUTING
MACHINE
ALAN TURING (1912–1954)
IN CONTEXT
BRANCH
Computer scienceBEFORE
1906 US electrical engineer
Lee De Forest invents the
triode valve, the mainstay of
early electronic computers.1928 German mathematician
David Hilbert formulates the
“decision problem,” asking if
algorithms can deal with all
kinds of input.AFTER
1943 Valve-based Colossus
computers, using some of
Turing’s code-breaking ideas,
begin work at Bletchley Park.1945 US-based mathematician
John von Neumann describes
the basic logical structure, or
architecture, of the modern
stored-program computer.1946 The first general-purpose
electronic programmable
computer, ENIAC, based
partly on Turing’s concepts,
is unveiled.I
magine sorting 1,000 random
numbers, for example 520, 74,
2395, 4, 999..., into ascending
order. Some kind of automatic
procedure could help. For instance:
A Compare the first pair of numbers.
B If the second number is lower,
swap the numbers, go back to A.
If it is the same or higher, go to C.
C Make the second number of the
last pair the first of a new pair. If
there is a next number, make it the
second number of the pair, go to B.
If there is no next number, finish.This set of instructions is a
sequence known as an algorithm.
It begins with a starting condition
or state; receives data or input;
executes itself a finite number of
times; and yields a finished result,
or output. The idea is familiar to
any computer programmer today.
It was first formalized in 1936,
when British mathematician and
logician Alan Turing conceived
of machines now known as
Turing machines to perform such
procedures. His work was initiallyA Turing machine
can, with the right
instructions, compute
the solution to any
solvable algorithm.This is a universal
computing machine.Varied tasks
can be solved using
different sets of instructions
in a programmable
device.Computing the
answers to many number
problems can be reduced
to a series of mathematical
steps, or algorithm.