Computer System Computer System HardwareHardware

Input DevicesInput DevicesInput devices enable a user to Input devices enable a user to input data and commands to the input data and commands to the computer to be processed.computer to be processed.

Input Device – The Input Device – The KeyboardKeyboard

The keyboard is the most widely used input The keyboard is the most widely used input device.device. As you press keys on the keyboard, an electrical As you press keys on the keyboard, an electrical

signal representing that key is sent to the computer.signal representing that key is sent to the computer. Keyboards are divided into sectionsKeyboards are divided into sections

Input Devices—The Input Devices—The Keyboard (cont.)Keyboard (cont.)

Typewriter keys:Typewriter keys: The standard alphabetic and The standard alphabetic and numeric characters you would find on a typewriternumeric characters you would find on a typewriter

Function keys:Function keys: Special keys that perform some Special keys that perform some specific function for the application being runspecific function for the application being run

Numeric keypad:Numeric keypad: Used for mathematical Used for mathematical operationsoperations

Directional keys:Directional keys: Used to move the cursor Used to move the cursor around the screenaround the screen

Input Devices—The Input Devices—The MouseMouse

The mouse is a pointing The mouse is a pointing device that rolls around on a device that rolls around on a flat surface and controls the flat surface and controls the location of the pointer on the location of the pointer on the screen.screen.

The mouse performs the The mouse performs the following functions:following functions: Pointing:Pointing: Placing the on- Placing the on-

screen pointer at a screen pointer at a specific placespecific place

Clicking:Clicking: Pressing and Pressing and releasing the mouse releasing the mouse buttonbutton

Input Devices—The Input Devices—The Mouse (cont.)Mouse (cont.)

Mouse functions (cont.)Mouse functions (cont.) Dragging:Dragging: Holding down the mouse Holding down the mouse

button and dragging an object to a new button and dragging an object to a new location by dragging the mouselocation by dragging the mouse

Double-clicking:Double-clicking: Pressing and Pressing and releasing the mouse button twice very releasing the mouse button twice very quicklyquickly

Right-clicking:Right-clicking: Pressing the right Pressing the right mouse buttonmouse button

Other Pointing DevicesOther Pointing Devices

Other devices that Other devices that control the on-screen control the on-screen pointer:pointer: Trackball:Trackball: This is like This is like

a mouse turned upside a mouse turned upside down. You roll a ball down. You roll a ball around with your around with your fingers to control the fingers to control the location of the pointer.location of the pointer. These frequently are These frequently are

found on notebook found on notebook computers.computers.

Other Pointing Devices Other Pointing Devices (cont.)(cont.)

Joystick and wheel:Joystick and wheel: Joysticks consist of a Joysticks consist of a metal or plastic metal or plastic handle mounted on a handle mounted on a base that you can base that you can move in any direction move in any direction to move the pointer or to move the pointer or other object.other object. These typically are These typically are

used for video used for video games.games.

Most have buttons Most have buttons that can be pushed that can be pushed or clicked to or clicked to control input/output.control input/output.

Other Input DevicesOther Input Devices Pointing stick:Pointing stick: A pressure- A pressure-

sensitive device that sensitive device that resembles a pencil eraser; resembles a pencil eraser; found mostly on notebook found mostly on notebook computerscomputers

Graphics tablet:Graphics tablet: A flat A flat drawing surface connected to drawing surface connected to the computerthe computer The user draws on the The user draws on the

surface, and the figures or surface, and the figures or writing on the tablet can writing on the tablet can be input to the computer be input to the computer for processing.for processing.

Other Input Devices Other Input Devices (cont.)(cont.)

Touch display:Touch display: Screens that contain Screens that contain pictures or shapes that the user can pictures or shapes that the user can press to input that datapress to input that data

Stylus/digital pen:Stylus/digital pen: Used with mobile Used with mobile devices to input datadevices to input data

Touchpad:Touchpad: Used mostly in Used mostly in laptop/notebook computerslaptop/notebook computers

Other Input Devices Other Input Devices (cont.)(cont.)

Audio/voice input:Audio/voice input: Inputting sound Inputting sound and/or voiceand/or voice These usually require a microphone These usually require a microphone

and special voice recognition software and special voice recognition software to be installed on the computer.to be installed on the computer.

Other Input Devices Other Input Devices (cont.)(cont.)

Scanners:Scanners: Devices that can convert a Devices that can convert a graphical image into a digital image and graphical image into a digital image and input it to the computer input it to the computer Types of scanners includeTypes of scanners include

Image scanners for scanning images and textImage scanners for scanning images and text Bar code scanners to read product bar codesBar code scanners to read product bar codes Magnetic scanners to read the magnetic strip Magnetic scanners to read the magnetic strip

on a credit cardon a credit card

Other Input Devices Other Input Devices (cont.)(cont.)

Digital cameras:Digital cameras: Used to take Used to take pictures and store them on a magnetic pictures and store them on a magnetic disk instead of on filmdisk instead of on film Their images can be input directly into Their images can be input directly into

the computer.the computer. Video input:Video input: Input from a camcorder Input from a camcorder

or VCR using video capture cardsor VCR using video capture cards

Other Input Devices Other Input Devices (cont.)(cont.)

Biometric input:Biometric input: Uses fingerprint, face, Uses fingerprint, face, handwriting, and voice for identificationhandwriting, and voice for identification

ProcessProcessIn computing, a In computing, a processprocess is an is an instance of a computer program, instance of a computer program, consisting of one or more threads, consisting of one or more threads, that is being sequentially executed that is being sequentially executed by a computer system that has the by a computer system that has the ability to run several computer ability to run several computer programs concurrently.programs concurrently.

Process (cont.)Process (cont.)

A computer program itself is just a passive A computer program itself is just a passive collection of instructions, while a process is the collection of instructions, while a process is the actual execution of those instructions. Several actual execution of those instructions. Several processes may be associated with the same processes may be associated with the same program; for example, opening up several program; for example, opening up several instances of the same program often means instances of the same program often means more than one process is being executed. In more than one process is being executed. In the computing world, processes are the computing world, processes are formallyformally defined by the operating system (OS) running defined by the operating system (OS) running them and so may differ in detail from one OS to them and so may differ in detail from one OS to another. another.

Process (cont.)Process (cont.) A single computer A single computer processorprocessor

executes one or more (multiple) executes one or more (multiple) instructions at a time (per clock instructions at a time (per clock cycle), one after the other (this is a cycle), one after the other (this is a simplification; for the full story, see simplification; for the full story, see superscalar CPU architecturesuperscalar CPU architecture). ).

To allow users to run several programs To allow users to run several programs at once (e.g., so that processor time is at once (e.g., so that processor time is not wasted waiting for input from a not wasted waiting for input from a resource), single-processor computer resource), single-processor computer systems can perform time-sharing. systems can perform time-sharing.

Process (cont.)Process (cont.)

Time-sharing allows processes to switch Time-sharing allows processes to switch between being executed and waiting (to between being executed and waiting (to continue) to be executed. In most cases this is continue) to be executed. In most cases this is done very rapidly, providing the illusion that done very rapidly, providing the illusion that several processes are executing 'at once'. several processes are executing 'at once'. (This is known as concurrency or (This is known as concurrency or multiprogramming.) Using more than one multiprogramming.) Using more than one physical processor on a computer, permits physical processor on a computer, permits truetrue simultaneous execution of more than one simultaneous execution of more than one stream of instructions from different processes, stream of instructions from different processes, but time-sharing is still typically used to allow but time-sharing is still typically used to allow more than one process to run at a time. more than one process to run at a time.

Process (cont.)Process (cont.)

(Concurrency is the term generally used to (Concurrency is the term generally used to refer to several independent processes sharing refer to several independent processes sharing a single processor; simultaneously is used to a single processor; simultaneously is used to refer to several processes, each with their own refer to several processes, each with their own processor.) Different processes may share the processor.) Different processes may share the same set of instructions in memory (to save same set of instructions in memory (to save storage), but this is not known to any one storage), but this is not known to any one process. Each execution of the same set of process. Each execution of the same set of instructions is known as an instructions is known as an instanceinstance— a — a completely separate instantiation of the completely separate instantiation of the program. program.

OutputOutputOutput devices enable the Output devices enable the computer to give or show you the computer to give or show you the results of its processingresults of its processing

Output Devices—MonitorsOutput Devices—Monitors

MonitorsMonitors are used to display video are used to display video output to a user.output to a user.

Monitors may be monochromatic or Monitors may be monochromatic or color.color. Monochromatic monitors display output Monochromatic monitors display output

in a single-color display.in a single-color display.

Output Devices—Monitors Output Devices—Monitors (cont.)(cont.)

Factors that influence the quality of a Factors that influence the quality of a monitormonitor Screen size: The diagonal Screen size: The diagonal

measurement in inches of the display measurement in inches of the display areaarea

Resolution: The number of pixels that Resolution: The number of pixels that can be displayed in the display areacan be displayed in the display area

Dot pitch: The distance between each Dot pitch: The distance between each pixel in the display areapixel in the display area

Typical Computer MonitorTypical Computer Monitor

This figure shows a This figure shows a typical computer typical computer monitor on a swivel monitor on a swivel stand that can be stand that can be adjusted for adjusted for viewing comfort.viewing comfort.

LCD

Gas plasma

Output Devices—PrintersOutput Devices—Printers

Printers are used to create a hard copy Printers are used to create a hard copy of a document or image.of a document or image. Printers vary by speed, quality, and Printers vary by speed, quality, and

price.price.

Output Devices—Printers Output Devices—Printers (cont.)(cont.)

The most popular types of printers areThe most popular types of printers are Laser:Laser: Produce images using the same Produce images using the same

techniques as copier machinestechniques as copier machines Ink jet:Ink jet: Use fine nozzles to spray ink onto Use fine nozzles to spray ink onto

the page as the paper passes throughthe page as the paper passes through Dot matrix:Dot matrix: Work similarly to a typewriter in Work similarly to a typewriter in

that ink is transferred to the paper by some that ink is transferred to the paper by some part of the printer striking a ribbon to transfer part of the printer striking a ribbon to transfer an imagean image

Laser PrinterLaser Printer

This figure provides an overview of a This figure provides an overview of a laser printer.laser printer.

Ink Jet PrinterInk Jet Printer

This figure provides an overview of an ink This figure provides an overview of an ink jet printer.jet printer.

Other Types of Output Other Types of Output DevicesDevices

Speakers and headsetsSpeakers and headsets Fax machines and fax modemsFax machines and fax modems Multifunctional devicesMultifunctional devices

Contain a variation of output optionsContain a variation of output options Data projectorsData projectors

StorageStorage

A A data storage devicedata storage device is a device is a device for recording (storing) information for recording (storing) information (data) (data)

Magnetic Storage Magnetic Storage DevicesDevices

Floppy disks:Floppy disks: Small, portable disks that hold a Small, portable disks that hold a limited amount of datalimited amount of data

Hard disks:Hard disks: Large-capacity and fast-access Large-capacity and fast-access storage devicesstorage devices

Zip disks:Zip disks: Auxiliary storage devices that can Auxiliary storage devices that can hold large quantities of data and can be portablehold large quantities of data and can be portable

Magnetic tape drives:Magnetic tape drives: Used for making system Used for making system backups and storing large quantities of databackups and storing large quantities of data

Optical Storage DevicesOptical Storage Devices

CD-DA:CD-DA: Audio CD Audio CD CD-R:CD-R: This drive This drive

allows you to read allows you to read and to write to a and to write to a compact diskcompact disk

CD-ROM:CD-ROM: Can hold Can hold large amounts of large amounts of data, but is read-data, but is read-only accessonly access

Optical Storage Devices Optical Storage Devices (cont.)(cont.)

CD-RW:CD-RW: Can be written on several times Can be written on several times DVD-ROM:DVD-ROM: Read-only DVD format Read-only DVD format DVD-R:DVD-R: Similar to CD, but holds more data; Similar to CD, but holds more data;

read-onlyread-only DVD-RW:DVD-RW: Can be written on several times Can be written on several times PhotoCDPhotoCD: Used for storing digital : Used for storing digital

photographs on a CDphotographs on a CD

Solid-State Storage Solid-State Storage MediaMedia

Non-volatile Non-volatile removable mediaremovable media

Miniature mobile Miniature mobile mediamedia Uses integrated Uses integrated

circuitscircuits USB flash driveUSB flash drive

Connects to the Connects to the computer via a computer via a USB portUSB port