Beginnings of a revolution - The Computing Universe: A Journey through a Revolution - page 7

Processor

Central Control
Unit (CC)

Input (I)

Memory (M)

Central Arithmetic
Unit (CA)

Output (O)

Fig. 1.10 The von Neumann Architecture. The main building blocks of all computers are the input,
output, memory, and processor. The input (typically now a keyboard or a mouse) feeds data into the
computer. This information is encoded by binary numbers and stored in the memory. The processor
then fetches the information, decodes it, and performs the required calculations. The results are put
back in the memory, where they can be read by the output device (typically a monitor, printer, or
even a loudspeaker). The processor consists of two components: the Central Control Unit (CC) and
the Central Arithmetic Unit (CA), now known as the Arithmetical and Logical Unit (ALU).

for its operations. As we shall see in Chapter 2 , binary, base-2 arithmetic is
much better suited to efficient and simple electronic implementations of arith-
metic and logic operations.
How does this von Neumann architecture relate to Turing's ideas about
universality? Before the war, Turing had spent time in Princeton and von
Neumann was well aware of the groundbreaking paper on theoretical comput-
ing machines he had completed as a student in Cambridge, UK. The memory,
input, and output of von Neumann's abstract architecture are logically equiva-
lent to the tape of a Universal Turing Machine, and the arithmetic and central
control units are equivalent to the read/write component of Turing's logical
machine. This means that no different computer design can do any different
calculations than a machine built according to von Neumann's architecture.
Instead of coming up with new architectures, computer engineers could spend
their time optimizing and improving the performance of the von Neumann
design. In fact, as we will see later, there are ways of improving on his design by
eliminating the so-called von Neumann bottleneck - in which all instructions
are read and executed serially, one after another - by using multiple processors
and designing parallel computers .

The global EDVAC diaspora

There were thirty-two people on the original mailing list for the “Report
on the EDVAC” but news of the report soon spread far and wide. With World
War II having come to an end, scientists were once again able to travel inter-
nationally, and by early 1946 the Moore School had already had several visi-
tors from Britain. The first visitor from the United Kingdom to the Moore
School was a New Zealander named Leslie Comrie ( B.1.3 ). Comrie had a long-
time interest in astronomy and scientific computation, and during the war he
had led a team of scientists to computerize such things as bombing tables for
the Allied Air Force. Remarkably, after his visit to see the ENIAC, Comrie was
allowed to take a copy of the EDVAC report back to England. Back in England,
he went to visit Maurice Wilkes (see Timeline) in Cambridge. Wilkes was a
mathematical physicist who had returned from war service and was trying to

B.1.3 Leslie Comrie (1893-1950)
was an astronomer and an expert
on numerical calculations. He vis-
ited the Moore School in 1946 and
brought the first copy of the EDVAC
report back to Britain.