Introduction to Java Programming - Building Java Programs: A Back to Basics Approach - page 3

Knuth is describing a thought process that is common to most of computer science,
which he refers to as algorithmic thinking. We study programming not because it
is the most important aspect of computer science, but because it is the best way to
explain the approach that computer scientists take to solving problems.
The concept of algorithms is helpful in understanding what a computer is and
what computer science is all about. The Merriam-Webster dictionary defines the
word “computer” as “one that computes.” Using that definition, all sorts of devices
qualify as computers, including calculators, GPS navigation systems, and children's
toys like the Furby. Prior to the invention of electronic computers, it was common to
refer to humans as computers. The nineteenth century mathematician Charles Peirce,
for example, was originally hired to work for the U.S. government as an “Assistant
Computer” because his job involved performing mathematical computations.
In a broad sense, then, the word computer can be applied to many devices. But
when computer scientists refer to a computer, we are usually thinking of a universal
computation device that can be programmed to execute any algorithm. Computer sci-
ence, then, is the study of computational devices and the study of computation itself,
including algorithms.
Algorithms are expressed as computer programs, and that is what this topic is all
about. But before we look at how to program, it will be useful to review some basic
concepts about computers.
Hardware and Software
A computer is a machine that manipulates data and executes lists of instructions
known as programs.
Program
A list of instructions to be carried out by a computer.
One key feature that differentiates a computer from a simpler machine like a cal-
culator is its versatility. The same computer can perform many different tasks (play-
ing games, computing income taxes, connecting to other computers around the
world), depending on what program it is running at a given moment. A computer can
run not only the programs that exist on it currently, but also new programs that
haven't even been written yet.
The physical components that make up a computer are collectively called
hardware. One of the most important pieces of hardware is the central processing
unit, or CPU. The CPU is the “brain” of the computer: It is what executes the instruc-
tions. Also important is the computer's memory (often called random access memory,
or RAM, because the computer can access any part of that memory at any time). The
computer uses its memory to store programs that are being executed, along with their
data. RAM is limited in size and does not retain its contents when the computer is
turned off. Therefore, computers generally also use a hard disk as a larger permanent
storage area.