Managing Information Technology

20 Part I • Information Technology

Basic Components of Computer Systems

For historical completeness, we should note that there are
really two distinct types of computers—digital and analog.
Digital computers operate directly on numbers, or digits,
just as humans do. Analog computers manipulate some
analogous physical quantity, such as voltage or shaft rota-
tion speed, which represents (to some degree of accuracy)
the numbers involved in the computation. Analog comput-
ers have been most useful in engineering and process-
control environments, but digital machines have largely
replaced them even in these situations. Thus, all of our dis-
cussion in this book relates to digital computers.

Underlying Structure

Today’s computers vary greatly in size, speed, and details
of their operation—from handheld microcomputers costing
around $100 to supercomputers with price tags of more
than $50 million. Fortunately for our understanding, all
these machines have essentially the same basic logical
structure (as represented in Figure 2.1). All computers,
whether they are microcomputers from Dell or mainframes
from IBM, are made up of the same set of six building
blocks: input, output, memory, arithmetic/logical unit, con-
trol unit, and files. Our discussion of how computers work
will focus on these six blocks and their interrelationships.
In addition to the blocks themselves, Figure 2.1 also
includes two types of arrows. The broad arrows represent
the flows of data through the computer system, and the
thin arrows indicate that each of the other components is
controlled by the control unit. A dashed line encircles the

control unit and the arithmetic/logical unit. These two

blocks together are often referred to as the central pro-

cessing unit, orCPU,or as the processor.

Input/Output

To use a computer, we must have some means of entering

data into the computer for it to use in its computations.

There are a wide variety of input devices, and we will men-

tion only the most commonly used types. The input

devices that you as a manager are most likely to use are a

microcomputer keyboard and a mouse. We will talk more

about microcomputers (PCs) later, but they include all of

the building blocks shown in Figure 2.1.

Aterminalis a simpler device than a PC; it is

designed strictly for input/output and does not incorporate

a processor (CPU), or at least not a general-purpose

processor. The terminal is connected to a computer via

some type of telecommunication line. Most terminals con-

sist of a keyboard for data entry and a monitor to show the

user what has been entered and to display the output from

the computer. Terminals are widely used by clerical per-

sonnel involved in online transaction processing (to be dis-

cussed in Chapter 5). Special types of terminals are also in

widespread use as computer input devices. Point-of-sale

terminals are in use at most retail stores, and automatic

teller machines (ATMs) are commonplace in the banking

industry. Like the standard terminals described earlier,

these special-purpose devices serve as both input and out-

put devices, usually incorporating a small built-in printer

to provide a hard-copy record of the transaction.

Voice input to computers is another input option,

although the accuracy of speech recognition softwareis

still less than perfect, with the best packages achieving

recognition accuracy in the 95 to 99 percent range. With

these numbers, speech recognition software is a productiv-

ity-enhancing tool for users with limited typing skills,

disabilities, repetitive stress injuries from overusing a

computer keyboard, or no time to do anything except

dictate (such as medical doctors).

Some input methods read an original document

(such as a typed report or a check or deposit slip) directly

into the computer’s memory. Check processing is handled

this way in the United States through the magnetic ink

character recognition (MICR)input method. Checks

have the account number and bank number preprinted at

the bottom using strange-looking numbers and a special

magnetizable ink. After a check is cashed, the bank that

cashed it records the amount of the check in magnetizable

ink at the bottom of the check. A computer input device

called a magnetic ink character reader magnetizes the ink,

recognizes the numbers, and transmits the data to the

Control

Unit

Arithmetic/

Logical

Unit

Input Memory Output

CENTRAL PROCESSING UNIT

Files

FIGURE 2.1 The Logical Structure of Digital Computers