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Chapter 4

Information System Hardware

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What is a computer A computer is a device that is

1. Electronic2. Can store data3. Can store and follow a set of

software instructions, called a program.

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Input Devices An input device accepts data from outside

the computer and converts it into an electronic form the computer can understand.

Keyboard Pointing devices Scanner Touch screen Light pen/electronical pen/stylus (pen like instrument) Pen commuter (these input devices use pen

technology) Digitizer (digitizing) tablet/graphics tablet (this

instrument is used in computer aided design/CAD) Personal digital assistant (PDA)

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Output Devices An output device converts data from an

electronic form inside the computer to a form that can be used outside the computer.

Monitor (is a device that produces on screen text, graphics, & images)

Printer (is an instrument that produces on paper text & graphics, & images)

Plotter (is an instrument that produces on paper high quality graphic output)

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Primary Storage Primary storage, read and write storage,

also called internal storage, is the “memory”, or RAM, of the computer.

Primary storage, which is temporary storage, is dependent upon continuous electrical power. Any interruption of electrical power causes the contents of primary storage to be lost.

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Central Processing Unit (CPU) The CPU, or processor, carries out the

instructions of the program. It contains circuits that control the operations of the hardware an the circuitry that performs arithmetic and logical operations.

Data is transferred from primary storage to the CPU with the results sent back to primary storage.

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Secondary Storage Secondary storage, also called

auxiliary storage, stores data not currently being processed by the computer and represents permanent storage.

Data is usually transferred to and from Secondary storage.

Examples include hard disks, floppy disks, ZIP disks, CDROMs, and DVDs.

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Keyboards Most widely used input device. Possible physical problems include

Repetitive strain injuries Carpal tunnel syndrome

Ergonomically designed keyboards may improve user comfort and efficiency and reduce risk of injury.

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Pointing Devices Mouse Trackball Track point/pointing stick Track pad/touch pad Cursor (is an on screen symbol

that shows the current position of the pointing device)

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Other input devices Touch screen Light pen/electronic pen that are

used with Graphics tablet/Digitizer tablet

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Optical Scanning Input Devices Bar-code scanner

Universal Product Code (UPC) Flat bed, or page scanner

Automatic document feeder (ADF) scanner

Mark-sense readers

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Magnetic Scanning Input Devices Magnetic strip reader

Credit cards ID Cards

Magnetic Ink Character Recognition (MICR) – used at the bottom of all checks by the banking industry.

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Voice Input Devices

Uses a microphone connected to the computer and translates the spoken word to digital input.

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Video Input Devices Digital cameras that converts

photographic images in to digital format.

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Screens, Monitor, or CRT Key elements of a “screen” include:

Pixels – picture elements arranged as a pattern of dots.

Screen resolution – the number of pixels that can be displayed on a screen at one time.

Refresh rate – the number of times per second that screen “repaints” itself.

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Screens, or Monitor, or CRT (cont’d.) Types of monitors

Traditional “tube” monitors, or cathode (electronic gun) ray tube (CRT).

Flat-panel screens – most common type is liquid crystal display (LCD).

Screen projector used to display a computers output on a large screen.

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Printers Printer classifications

Impact printer Nonimpact printer Serial printers Line printers Page printers Letter-quality printers Draft-quality printers

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Desktop printers Ink-jet, or bubble-jet printer

Typically 200 to 300 characters per second

Laser printers Typically between 4 and 24 pages per

minute. Dot matrix printer

Typically between 200 and 300 characters per second.

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High volume printers Line printers

High end line printers can print as much as 3,600 lines per minute (at 60 lines per page, that is 60 page per minute) and can cost $50,000.

Page printers High end page printers can print as

much as 200 pages per minute and can cost $100,000.

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Other Output Devices Plotters Voice output devices – converting

digitized data into synthesized speech

Specialized devices for people with disabilities – can include large typeface screens, Braille display devices.

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Virtual Reality Virtual reality is the use of a

computer to produce realistic images and sounds in such a way that the user senses that he or she is a part of the scene.

Applications include architectural design, home remodeling, aircraft design, machine design, and more.

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Primary Storage Structure Input data is stored in primary

storage (memory) after it is received from an input device.

Output data is stored in primary storage before it is sent to an output device.

Without sufficient primary storage, it may not be possible to execute certain programs or use certain data.

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Primary Storage Structure (cont’d.) Silicon chips – integrated circuits Volatile storage – dependent upon

continuous power Random Access Memory (RAM)

Non-volatile storage Read-Only Memory (ROM)

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Primary Storage Structure (cont’d.) Binary representation

A combination of positive and negative electrical charges, represented by 1s and 0s when written to represent a character.

One “charge” is called a bit. Eight bits are required to represent a single

character, called a byte. The 256 possible (28) binary

combinations are defined in character set.

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Primary Storage Structure (cont’d.) Personal computer character set

ASCII – American Standard Code for Information Interchange

Mainframe computer character set EBCDIC – Extended Binary Coded Decimal

Interchange Code Though each contains 256 characters,

the definitions are not the same, so a “translator” is required for one machine type to “talk” with the other machine type.

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Primary Storage Structure (cont’d.) Storage capacities

Kilobyte (KB) or 1024 bytes (210) – approximately 1,000 bytes, thus the “kilo”

Megabyte (MB) or 1,048,756 bytes (220) Gigabyte (GB) or 1,073,741,824 bytes

(230) Terabyte (TB) or 1,099,511,627,776

bytes (240)

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Two Main Parts of a CPU Arithmetic-Logic Unit (ALU)

May add, subtract, multiply and divide two numbers. More complex operations are are completed by using sequences of the four basic operations.

Control Unit Analyzes and executes instructions in a

program. Instructions are brought in one at a time from primary storage.

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CPU Speed Early CPUs processed 8 or 16 bits at

a time. Current CPUs process 32 bits, and

some can process 64 or 128 bits at a time.

The “roadway” from primary storage to the CPU is the bus. Higher bus capacities mean faster computers.

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CPU Speed (cont’d.) Clock speed

Measured in megahertz (MHz) or gigahertz (GHz).

One MHz is one million cycles per second. One GHz is one billion cycles per second. Earliest IBM PCs ran at 4.77 MHz. Current PCs run at or above 2,000 MHz

(2 GHz).

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Types of Secondary Storage Magnetic Disk

Storage Floppy disk Hard disk ZIP disk

Disk organization Disk Head (or side) Track Cylinder

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Optical Disk Storage Compact disks (CDROMs) Writable Compact Disks (CD-RWs) Digital Video Disks or Digital

Versatile Disks (DVDs)

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Magnetic Tape Storage Data transferred to the tape via a

magnetic tape drive. Data on a tape can only be read

sequentially.