Computer System Hardware

Input Devices

Input devices enable a user to input data and commands to

the computer to be processed.

Input Device – The Keyboard

• The keyboard is the most widely used input device.– As you press keys on

the keyboard, an electrical signal representing that key is sent to the computer.

– Keyboards are divided into sections

Input Devices—The Keyboard (cont.)

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

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

• Numeric keypad: Used for mathematical operations

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

Input Devices—The Mouse

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

• The mouse performs the following functions:– Pointing: Placing the

on-screen pointer at a specific place

– Clicking: Pressing and releasing the mouse button

Input Devices—The Mouse (cont.)

• Mouse functions (cont.)– Dragging: Holding down the

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

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

– Right-clicking: Pressing the right mouse button

Other Pointing Devices

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

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

• These frequently are found on notebook computers.

Other Pointing Devices (cont.)– Joystick and

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

• These typically are used for video games.

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

Other Input Devices

• Pointing stick: A pressure-sensitive device that resembles a pencil eraser; found mostly on notebook computers

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

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

Other Input Devices (cont.)

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

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

• Touchpad: Used mostly in laptop/notebook computers

Other Input Devices (cont.)

• Audio/voice input: Inputting sound and/or voice– These usually require a

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

Other Input Devices (cont.)

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

•Image scanners for scanning images and text

•Bar code scanners to read product bar codes

•Magnetic scanners to read the magnetic strip on a credit card

Other Input Devices (cont.)

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

directly into the computer.

• Video input: Input from a camcorder or VCR using video capture cards

Other Input Devices (cont.)

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

ProcessIn computing, a process is an instance of a computer program, consisting of one or more threads, that is being sequentially executed by a computer system that has

the ability to run several computer programs concurrently.

Process (cont.)

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

Process (cont.)• A single computer processor executes one or more (multiple)

instructions at a time (per clock cycle), one after the other (this is a simplification; for the full story, see superscalar CPU architecture). To allow users to run several programs at once (e.g., so that processor time is not wasted waiting for input from a resource), single-processor computer systems can perform time-sharing. Time-sharing allows processes to switch between being executed and waiting (to continue) to be executed. In most cases this is done very rapidly, providing the illusion that several processes are executing 'at once'. (This is known as concurrency or multiprogramming.) Using more than one physical processor on a computer, permits true simultaneous execution of more than one stream of instructions from different processes, but time-sharing is still typically used to allow more than one process to run at a time. (Concurrency is the term generally used to refer to several independent processes sharing a single processor; simultaneously is used to refer to several processes, each with their own processor.) Different processes may share the same set of instructions in memory (to save storage), but this is not known to any one process. Each execution of the same set of instructions is known as an instance— a completely separate instantiation of the program.

Output

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

Output Devices—Monitors

• Monitors are used to display video output to a user.

• Monitors may be monochromatic or color.– Monochromatic monitors display

output in a single-color display.

Output Devices—Monitors (cont.)

• Factors that influence the quality of a monitor– Screen size: The diagonal

measurement in inches of the display area

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

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

Typical Computer Monitor

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

LCD

Gas plasma

Output Devices—Printers

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

and price.

Output Devices—Printers (cont.)

• The most popular types of printers are– Laser: Produce images using the

same techniques as copier machines

– Ink jet: Use fine nozzles to spray ink onto the page as the paper passes through

– Dot matrix: Work similarly to a typewriter in that ink is transferred to the paper by some part of the printer striking a ribbon to transfer an image

Laser PrinterThis figure provides an overview

of a laser printer.

Ink Jet PrinterThis figure provides an overview of

an ink jet printer.

Other Types of Output Devices

• Speakers and headsets• Fax machines and fax modems• Multifunctional devices

– Contain a variation of output options

• Data projectors

Storage

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

information (data)

Magnetic Storage Devices

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

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

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

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

Optical Storage Devices

• CD-DA: Audio CD• CD-R: This drive

allows you to read and to write to a compact disk

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

Optical Storage Devices (cont.)

• CD-RW: Can be written on several times

• DVD-ROM: Read-only DVD format• DVD-R: Similar to CD, but holds

more data; read-only• DVD-RW: Can be written on several

times• PhotoCD: Used for storing digital

photographs on a CD

Solid-State Storage Media

• Non-volatile removable media

• Miniature mobile media– Uses integrated

circuits• USB flash drive

– Connects to the computer via a USB port