AN EXAMPLE SYSTEM: WADING THROUGH THE JARGON

This book will introduce you to some of the vocabulary that is specific to computers.

This jargon can be confusing, imprecise, and intimidating. We believe that

with a little explanation, we can clear the fog.

For the sake of discussion, we have provided a facsimile computer advertisement

(see Figure 1.1). The ad is typical of many in that it bombards the reader

with phrases such as “64MB SDRA

kilobyte (1KB) of memory is typically 1,024 bytes of memory rather than 1,000

bytes of memory. However, a 1GB disk drive might actually be 1 billion bytes

instead of 230 (approximately 1.7 billion). You should always read the manufacturer’s

fine print just to make sure you know exactly what 1K, 1KB, or 1G represents.

When we want to talk about how fast something is, we speak in terms of fractions

of a second—usually thousandths, millionths, billionths, or trillionths. Prefixes

for these metrics are given in the right-hand side of Figure 1.2. Notice that

the fractional prefixes have exponents that are the reciprocal of the prefixes on

the left side of the figure. Therefore, if someone says to you that an operation

requires a microsecond to complete, you should also understand that a million of

those operations could take place in one second. When you need to talk about

how many of these things happen in a second, you would use the prefix mega-.

When you need to talk about how fast the operations are performed, you would

use the prefix micro-.

M,” “64-bit PCI sound card” and “32KB L1

cache.” Without having a handle on such terminology, you would be hard-pressed

to know whether the stated system is a wise buy, or even whether the system is

able to serve your needs. As we progress through this book, you will learn the

concepts behind these terms.

Before we explain the ad, however, we need to discuss something even more

basic: the measurement terminology you will encounter throughout your study of

computers.

It seems that every field has its own way of measuring things. The computer

field is no exception. So that computer people can tell each other how big something

is, or how fast something is, they must use the same units of measure. When

we want to talk about how big some computer thing is, we speak of it in terms of

thousands, millions, billions, or trillions of characters. The prefixes for terms are

given in the left side of Figure 1.2. In computing systems, as you shall see, powers

of 2 are often more important than powers of 10, but it is easier for people to

understand powers of 10. Therefore, these prefixes are given in both powers of 10

and powers of 2. Because 1,000 is close in value to 2

10

(1,024), we can approximate

powers of 10 by powers of 2. Prefixes used in system metrics are often

applied where the underlying base system is base 2, not base 10. For example, a