Computer Organization and Design the Hardware Software Interface-3rded2004

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1 1 Introdudlon

Classes o Computing pplications and Their

Characteristics

Although a common set of hardware technologies (discussed in Sections 1.3 and

1.4) is used in computers ranging from smart home appliances to ce ll phones to

the larges t supercomputers these different app lica tions have different design

requirements and empl oy the core hardware technologies in different ways.

Broadly speakín g, computers are used in three different classes of applications.

Desktop computers are possibly the best-known form of computing and are

characteri zed by the personal computer, which most readers of thi s book have

probably used ex tensive ly. Desktop computers emphasíze delivering good performan ce to a single user at low cost and usually are used to execute third -partyso ft

ware, also ca lled shrink-wrap software. Desktop computing is one of the largest

markets for computers, and the evolution of many computing technologíes is

driven by this class of computing, which is onl y about 30 years old

Servers are the rnodern form of what was once mainframes, minicomputers,

and supercomputers, and are usuall y accessed only vía a network. Servers are or i

ented to ca rrying large workloads, which may consíst of either single co mplex

applications, usually a scientific or enginee ring application, or handling many

small jobs, such as would occur in building a large Web server. These app lica tions

are often based on softwa re from another source (such as a database or simulation

system), but are often mod ified or customized for a particular functi on. Servers

are built from the same basic technology as desktop computers but provide for

greater expa ndability ofbo th computing and input output capacity. As we will see

in the Chapter 4, the performance of a server ca n be measured in several different

ways, depending on the application of interes t. In ge nera l servers also place a

greater emphasis on dependability, since a crash is usually more cos tly than it

would be on a single- user desktop computer.Se rve rs span the widest range in cost and capability. At the low end, a server

may be little more than a desktop machine without a screen or keyboard and with

a cost of a thousand dollars. These low-end servers are typica lly used for file stor

age, small business applications, or simple web serving. At the other ex treme are

supercomputers, which at the present co nsist of hundreds to thousands of pro

cessors, and usually giga bytes to terabytes of memory and terabytes to petabytes

of storage, and cost millions to hundreds of rnillions of dollars. Supercomputers

are usually used for high-end scientific and engineer in g calculations such as

wea ther forecasting, oil exploration , protein structure determination, and other

large-scale problems. Alth ough such supercomputers represent the peak of com

puting capability they are a relatively small fraction of the servers and a relatively

small fraction of the overa ll computer market in terms of total revenu e.

Embedded computers are the larges t class of computers and span the wid es t

range of applications and performance. Embedded computers include the micro

processors found in your washin g machine and ca r the computers in a ce ll phone

5

desktopcomputer A com-

puter designed for use by an

individual, usually incorpora t

ing a graphics display, keyboard,

and mouse.

Server A computer used for

running larger programs for

multiple users often simulta

neously and typically accessed

only via a network.

supercomputer A class of

computers with the highest per

formance and cos t; they are

configured as servers and typi

cally cost millions of dollars.

terabyte Originally

1,099,511,627,776 (240) bytes,

although sorne communications

and secondary storage systemshave redefined it to mean

1,000,000,000,000 ( 10 12) bytes.

embedded computer A com-

puter inside another device used

for rUlUling one predetermined

application or collection of soft

ware.

Computer Organization and Design the Hardware Software Interface-3rded2004

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