Hardware Reference
In-Depth Information
While Eckert and Mauchley were working on the EDVAC, one of the people
involved in the ENIAC project, John von Neumann, went to Princeton's Institute of
Advanced Studies to build his own version of the EDVAC, the
IAS machine
.Von
Neumann was a genius in the same league as Leonardo Da Vinci. He spoke many
languages, was an expert in the physical sciences and mathematics, and had total
recall of everything he ever heard, saw, or read. He was able to quote verbatim
from memory the text of topics he had read years earlier. At the time he became
interested in computers, he was already the most eminent mathematician in the
world.
It was soon apparent to him that programming computers with huge numbers
of switches and cables was slow, tedious, and inflexible. He came to realize that
the program could be represented in digital form in the computer's memory, along
with the data. He also saw that the clumsy serial decimal arithmetic used by the
ENIAC, with each digit represented by 10 vacuum tubes (1 on and 9 off) could be
replaced by using parallel binary arithmetic, something Atanasoff had realized
years earlier.
The basic design, which he first described, is now known as a
von Neumann
machine
. It was used in the EDSAC, the first stored-program computer, and even
now, more than half a century later, is still the basis for nearly all digital com-
puters. This design, and the IAS machine, built in collaboration with Herman
Goldstine, has had such an enormous influence that it is worth describing briefly.
Although Von Neumann's name is always attached to this design, Goldstine and
others made major contributions to it as well. A sketch of the architecture is given
in Fig. 1-5.
Memory
Input
Arithmetic
logic unit
Control
unit
Output
Accumulator
Figure 1-5.
The original von Neumann machine.
The von Neumann machine had five basic parts: the memory, the arithmetic
logic unit, the control unit, and the input and output equipment. The memory con-
sisted of 4096 words, a word holding 40 bits, eacha0ora1. Each word held ei-
ther two 20-bit instructions or a 40-bit signed integer. The instructions had 8 bits
devoted to telling the instruction type and 12 bits for specifying one of the 4096
