19 Nov
2003
19 Nov
'03
7:50 a.m.
From Daniel I. A. Cohen's book, Introduction To
Compuer Theory,
pp 788
>Definition. If a Turning Machine (TM) has the
property that for every
word
>it accepts, at the time it halts, it leaves one
solid string of a's and
b's on
>its Tape starting in cell i, we call it a computer.
The input string we
call
>the input (or, string of input numbers), and we
identify it as a sequence
>of nonnegative integers. The string left on the Tape we call the output
>and identify it also as a sequence of nonnegative integers.
The discussion continues,
"Now we finally know what a computer is. Those expensive boxes of
electronics sold as computers are only approximations to the real McCoy.
For one thing, they almost never come with an infinite memory like a true
TM."
William R. Buckley