Chapter 5

Computing Components

(modified by Erin Chambers)

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Computer Components

Consider the following ad

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Sizes in Perspective

Admiral Grace Murray Hopper

A coil of wire nearly 1,000 feet long

Distance traveled by an electron along the wire
in the space of a microsecond

A short piece of wire

In the space of a nanosecond

A bag containing grains of pepper

In the space of a picosecond

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Sizes in Perspective

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Stored-Program Concept

Figure 5.1 The von Neumann architecture

Memory

Memory is a collection of cells,
each with a unique physical address

The term '64-bit processor' means that the CPU can address 264 different positions in memory

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Arithmetic/Logic Unit

Performs basic arithmetic operations such as adding

Performs logical operations such as AND, OR, and NOT

Most modern ALUs have a small amount of special storage units called registers

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Input/Output Units

Input Unit A device through which data and programs from the outside world are entered into the computer

Keyboard, the mouse, and scanning devices

Output unit A device through which results stored in the computer memory are made available to the outside world

Printers and video display terminals

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Control Unit

Control unit The organizing force
in the computer

There are two registers in the control unit

The instruction register (IR) contains the instruction that is being executed

The program counter (PC) contains the address of the next instruction to be executed

ALU and the control unit called the Central Processing Unit, or CPU

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Flow of Information

The parts are connected to one another by a collection of wires called a bus

Figure 5.2 Data flow through a von Neumann architecture

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The Fetch-Execute Cycle

Fetch the next instruction

Decode the instruction

Get data if needed

Execute the instruction

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Figure 5.3 The Fetch-Execute Cycle

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RAM and ROM

RAM stands for Random Access Memory

Inherent in the idea of being able to access each location is the ability to change the contents of each location

ROM stands for Read Only Memory

The contents in locations in ROM cannot be changed

RAM is volatile, ROM is not

This means that RAM does not retain its bit configuration when the power is turned off,
but ROM does

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Secondary Storage Devices

Because most of main memory is volatile and limited, it is essential that there be other types of storage devices where programs and data can be stored when they are no longer being processed

Secondary storage devices can be installed within the computer box at the factory or added later as needed

Magnetic Tape

The first truly mass auxiliary storage device was the magnetic tape drive

Figure 5.4 A magnetic tape

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Magnetic Disks

A read/write head travels across a spinning magnetic disk, retrieving or recording data

Figure 5.5
The organization of a magnetic disk

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Compact Disks

A CD drive uses a laser to read information stored optically on a plastic disk

CD-ROM is Read-Only Memory

DVD stands for Digital Versatile Disk

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Touch Screens

Touch screen A computer monitor that can respond to the user touching the screen with a stylus or finger

There are four types

Resistive

Capacitive

Infrared

Surface acoustic wave (SAW)

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Touch Screens

Resistive touch screen A screen made up of two layers of electrically conductive material.

One layer has vertical lines, the other has horizontal lines.

When the top layer is pressed, it comes in contact with the second layer which allows electrical current to flow.

The specific vertical and horizontal lines that make contact dictate the location on the screen that was touched.

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Touch Screens

Capacitive touch screen A screen made up of a laminate applied over a glass screen.

The laminate conducts electricity in all directions, and a very small current is applied equally on the four corners.

When the screen is touched, current flows to the finger or stylus.

The location of the touch on the screen is determined by comparing how strong the flow of electricity is from each corner.

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Touch Screens

Infrared touch screen A screen with crisscrossing horizontal and vertical beams of infrared light

Sensors on opposite sides of the screen detect the beams.

When the user breaks the beams by touching the screen, the location of the break can be determined.

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Touch Screens

Surface acoustic wave (SAW) A screen with crisscrossing high frequency sound waves across the horizontal and vertical axes.

When a finger touches the surface, the corresponding sensors detect the interruption and determine the location of the touch.

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Synchronous processing

One approach to parallelism is to have multiple processors apply the same program to multiple data sets

Figure 5.7 Processors in a synchronous computing environment

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Pipelining

Arranges processors in tandem, where each processor contributes one part to an overall computation

Figure 5.8 Processors in a pipeline

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Independent Processing
with Shared Memory

Figure 5.9 A shared-memory configuration of processors

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Jones & Bartlett Publishers

2002-06-08T19:44:04