Introduction - Java Software Solutions: Foundations of Program Design - page 2

1.1 Computer Processing

We begin our exploration of computer systems with an overview of computer
processing, defining some fundamental terminology and showing how the key
pieces of a computer system interact.
A computer system is made up of hardware and software. The

hardware com-
ponents of a computer system are the physical, tangible pieces that support the
computing effort. They include chips, boxes, wires, keyboards, speakers, disks,
memory cards, USB flash drives (also called jump drives), cables, plugs, printers,
mice, monitors, routers, and so on. If you can physically touch it and it can be
considered part of a computer system, then it is computer hardware.
The hardware components of a computer are essentially useless
without instructions to tell them what to do. A

KEY CONCEPT
A computer system consists of
hardware and software that work in
concert to help us solve problems.

program is a series of
instructions that the hardware executes one after another. Software

consists of programs and the data those programs use. Software is
the intangible counterpart to the physical hardware components.
Together they form a tool that we can use to help solve problems.
The key hardware components in a computer system are

central processing unit (CPU)

■

input/output (I/O) devices

■

main memory

■

secondary memory devices
Each of these hardware components is described in detail in the next section. For
now, let's simply examine their basic roles. The

■

central processing unit (CPU) is
the device that executes the individual commands of a program. Input/output

(I/O) devices , such as the keyboard, mouse, and monitor, allow a human being to
interact with the computer.
Programs and data are held in storage devices called memory, which fall into
two categories: main memory and secondary memory. Main memory is the storage
device that holds the software while it is being processed by the CPU. Secondary
memory devices store software in a relatively permanent manner. The most impor-
tant secondary memory device of a typical computer system is the hard disk that
resides inside the main computer box. A USB flash drive is also an important sec-
ondary memory device. A typical USB flash drive cannot store nearly as much infor-
mation as a hard disk. USB flash drives have the advantage of portability; they can
be removed temporarily or moved from computer to computer as needed. Another
portable secondary memory device is the compact disc (CD).
Figure 1.1 shows how information moves among the basic hardware compo-
nents of a computer. Suppose you have an executable program you wish to run.