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2.1 / A BRIEF HISTORY OF COMPUTERS 17

KEY POINTS

◆ The evolution of computers has been characterized by increasing processor
speed, decreasing component size, increasing memory size, and increasing
I/O capacity and speed.
◆ One factor responsible for the great increase in processor speed is the
shrinking size of microprocessor components; this reduces the distance be-
tween components and hence increases speed. However, the true gains in
speed in recent years have come from the organization of the processor, in-
cluding heavy use of pipelining and parallel execution techniques and the
use of speculative execution techniques (tentative execution of future in-
structions that might be needed). All of these techniques are designed to
keep the processor busy as much of the time as possible.
◆ A critical issue in computer system design is balancing the performance of
the various elements so that gains in performance in one area are not hand-
icapped by a lag in other areas. In particular, processor speed has increased
more rapidly than memory access time. A variety of techniques is used to
compensate for this mismatch, including caches, wider data paths from
memory to processor, and more intelligent memory chips.

We begin our study of computers with a brief history.This history is itself interest-
ing and also serves the purpose of providing an overview of computer structure
and function. Next, we address the issue of performance. A consideration of the
need for balanced utilization of computer resources provides a context that is use-
ful throughout the book. Finally, we look briefly at the evolution of the two sys-
tems that serve as key examples throughout the book: the Intel x86 and ARM
processor families.

2.1 A BRIEF HISTORY OF COMPUTERS

The First Generation:Vacuum Tubes

ENIAC The ENIAC (Electronic Numerical Integrator And Computer), designed
and constructed at the University of Pennsylvania, was the world’s first general-
purpose electronic digital computer.The project was a response to U.S. needs during
World War II.The Army’s Ballistics Research Laboratory (BRL), an agency respon-
sible for developing range and trajectory tables for new weapons, was having diffi-
culty supplying these tables accurately and within a reasonable time frame.Without
these firing tables, the new weapons and artillery were useless to gunners.The BRL
employed more than 200 people who, using desktop calculators, solved the neces-
sary ballistics equations. Preparation of the tables for a single weapon would take
one person many hours, even days.