Computer:
Computer is an electronic machine that follows instructions, gets data from an input
device, directs processing of the data and directs information to an output device.
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Types of Computers
Personal computers
Minicomputers
Supercomputers
Servers
Personal computers
It can be defined as a small, relatively inexpensive computer designed for an individual
user.
Personal computers are desktop computers designed for an individual's use. They
run programs designed to help individuals accomplish their work more productively.
Minicomputers
It is a midsize computer.Minicomputers are multi-user systems that can handle the
computing needs of a smaller corporation or organization. Many people use them simultaneously
by means of remote terminals or personal computers.
Supercomputers
Supercomputer is a broad term for one of the fastest computers currently available.
Supercomputers
are very expensive. Supercomputers are ultra fast computers designed to process
hugh amounts of scientific data then display the underlying patterns that have been
discovered.
Servers
Servers are not designed to be used directly. They make programs and data available
for people hooked up to a computer network, a collection of computers connected
together so that they can exchange data.
Input Devices
An input device lets you communicate with a computer. You can use input
devices to enter information and issue commands. A keyboard, mouse, scanner, digital
camera, touch pads and joystick are examples of input devices.
Computer Input Devices:
Keyboard
Used to type data into the computer
This is most common input device today
Pointing Devices
Common pointing devices
Mouse - most common pointing device
Track ball Joystick
Scanner
A scanner allows you to scan documents, pictures, or graphics and view them on the
computer. You can also use software to edit the items you scan.
Used to put printed pictures and text into a computer
Converts an image into dots that the computer can understand
To scan text, optical character recognition (OCR) software is needed
Digital Camera
Used to take electronic pictures of an object
The pictures taken by a digital camera can be used directly by a computer
Microphone
Used to put sound into a computer
Need sound recording software
CD-ROM/DVD-ROM
Can be used to put both sound and images into a computer
Use a laser to read a Compact Disk (CD) or a DVD disk
Video Capture Card
Usually place inside the computer's case
Need a video source, either a video camera or video recorder
Out Devices
An output device displays information on a screen, creates printed copies
or generates sound. A monitor, printer, and speakers are examples of output devices.
Common Output Devices:
Monitors
Shows the processed information on a screen
A monitor uses a Picture Tube like a television with the image displayed
on the front of the tube,
which is called the screen.
Displays are flat and use plasma, LCD, active-matrix, or some other
technology.
Monitors used to be called Cathode Ray Tubes (CRTs) because of the picture tube,
which is a large vacuum tube.
A monitor or display produce a soft copy. When the device is turned off the information
goes away.
Printers
Printers produce a hard copy
The information is printed on paper and can be used when the device is off. It is
also called a printout.
Dot-matrix printers
Uses metal pins to strike an inked ribbon to make dots on a piece of paper.
Can see the dots that make up the letters or images.
Lowest print quality of all of the printers.
Very low in cost per page to use.
Rarely used today because of the poor print quality, but still used in business
to print multi-part forms.
Ink jet printers
Use drops of magnetic ink to produce dots on a page to produce text or images.
The print quality is almost the same as a laser printer's.
Problems with the ink
The ink is very expensive
The ink is water soluble and will run if the paper gets wet.
Very low in cost per page to use.
Highest cost per page of all the printers.
For producing color documents, it has the highest quality at a reasonable price.
Laser printers
How the laser printer produces an image
A laser or LEDs make dots on a light sensitive drum
Toner (very tiny particles of plastic) stick to the drum where the
dots where made
Paper is pressed against the drum and the toner is placed on the paper
The paper is heated and the toner melts into the paper
Produces the highest quality printout.
For black and white printouts, very low cost per page.
Printout is permanent.
Color laser printers are still fairly expensive.
Storage Devices
Computer stores information
The computer stores information as a string of zeros (0) and ones (1)
The standard string length is eight 0's or 1's in a row
This standard length is called a byte
A byte equals one character
- A character is a letter, number, or symbol -
it is about any thing that can be typed
on a keyboard
- There are 256 standard characters used by almost
all computers
Information size measurements
Kilobyte (KB)
-One kilobyte equals about 1024 bytes
Megabyte (MB)
-One megabyte equals about 1000 KB
-One megabyte equals about 1,000,000 bytes
Gigabyte (GB)
-One gigabyte equals about 1000 MB
-One gigabyte equals about 1,000,000 KB
-One gigabyte equals about 1,000,000,000 bytes
Common Storage Devices
Hard Drive
The hard drive is the primary device that a computer uses to store
information.
The hard drive stores programs, data files, saves files, and organizes
files.
The hard drive is located inside the computer case.
The hard drive, magnetically stores data on stacks of rotating disks
called platters.
Floppy Drive
The floppy drive stores and retrieves information on a floppy disk.
CD -ROM Drive
CD-ROM is a device that reads information stored on a compact disc.
CD-ROM stands for Compact Disc Read Only Memory.
One CD is equal to the space in over 40 floppy disc.
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