Lesson 2: Output Devices 

Unit 1: Definition of Output Devices

An output device is any piece of computer hardware equipment which converts information into human-readable form. It can be text, graphics, tactile, audio, and video.  Output devices are the peripherals of the computer that transfer information from the computer to the user. The output unit of the computer can be better understood by comparing it with the human body.

Some of the output devices are Visual Display Units (VDU) i.e. a Monitor, Printer, Graphic Output devices, Plotters, Speakers etc.

Unit 2: Reasons for Having an Output Device 
A computer can still function without an output device.  However, without an output device, there’s no way to determine what the computer is doing.  There is no indicator of errors, nor of the need for additional input.   For example, if you detach your monitor from your computer, the computer will still function, but it’s not going to be very helpful.

Unit 3: Examples of Output Devices 
(a) Monitor – This is the most common computer output device. It creates a visual display by the use of which users can view processed data.  Monitors come in various sizes and resolutions.

Common Types of Monitors
(i) Cathode Ray Tube
– this uses phosphorescent dots to generate the pixels that constitute displayed images.
(ii) Flat Panel Screen – this makes use of liquid crystals or plasma to produce output. Light is passed through the liquid crystals in order to generate pixels. All monitors depend on a video card, which is positioned either on the computer motherboard or in a special expansion slot. The video card sorts out the computer data into image details that the monitors can then show.

(b) Printer – this device generates a hard copy version of processed data, like documents and photographs. The computer transmits the image data to the printer, which then physically recreates the image, typically on paper.

Types of Printers
(i) Ink Jet
– this kind of printer sprays tiny dots of ink onto a surface to form an image.
(ii) Laser – this type utilises toner drums that roll through magnetized pigment, and then transfers the pigment onto a surface.
(iii) Dot Matrix – dot matrix printers utilise a print head to set images on a surface, using an ink ribbon. These printers were commonly used in the 1980s

(c) Speakers – speakers are attached to computers to facilitate the output of sound; sound cards are required in the computer for speakers to function. The different kinds of speakers range from simple, two-speaker output devices right the way up to surround-sound multi-channel units.

(d) Headset – this is a combination of speakers and microphone.  It is mostly used by gamers, and is also a great tool for communicating with family and friends over the internet using some VOIP program or other.

(e) Projector – this is a display device that projects a computer-created image onto another surface: usually some sort of whiteboard or wall. The computer transmits the image data to its video card, which then sends the video image to the projector. It is most often used for presentations, or for viewing videos.

(f) Plotter – this generates a hard copy of a digitally depicted design. The design is sent to the plotter through a graphics card, and the design is formed by using a pen.  It is generally used with engineering applications, and essentially draws a given image using a series of straight lines.

Unit 4: Structure of the Monitor
The features of the monitor are the screen, the cable, and the monitor screen size. The portion of the monitor that displays information is called the screen. Like a television screen, a computer screen can show still or moving pictures.

The monitor also has a connecting cable tethered to the system unit. This cable is called VGA (visual graphic array) cable. Based on their technology of display, there are two basic forms of monitors: CRT (cathode ray tube) monitors and the newer LCD (liquid crystal display) monitors.

Types of Monitors
Most computer monitors use a cathode-ray tube (CRT) as the display device. A CRT is a glass tube that is narrow at one end and opens to a flat screen at the other end. The two types are:

1. Monochrome Monitors; They display one colour for text and pictures, such as white, green, or amber, against a dark colour such as black, for the background.
2. Color Monitors: These types can display full colour for text and pictures. They use a mixture of red, green and blue to display any colour.

Unit 5: Types of Printers
There are various types of printers, depending on I the technology they use in printing on paper or other material medium. They can be categorised into two, namely; impact printers and non-impact printers.

Impact Printers
This type of printing devices creates an image by using some mechanism to physically press an inked ribbon against the paper, thereby causing the ink to be deposited on the page in the shape desired. It works just like the traditional typewriters. They tend to be noisy when they are in use.

Types of Impact Printers
There are three different types, namely:

1. Dot-Matrix Printers:
These types of printers form each character as a group of small dots, using a group of wires located in the printing element. They are also known as dot character printers.
2. Line Printers: They print line by line. The disadvantages of line printers are that they cannot print graphics, the print quality is low, and they are very noisy.
3. Character Printers: Character printers print one character at a time and hence they are slow printers.

Non-impact Printers
They are the type of printers that do not operate by striking a head against a ribbon. They work by applying ink on paper. They are the most commonly used types today.

Types of Non-impact printers
There are three types, namely:

1. Inject Printers: They create a digital image by propelling droplets of ink onto paper.
2. Laser Printers: They are electro photographic printers that use a cylindrical drum that rolls electrically charged ink onto the paper.
3. Thermal Printers: A thermal printer produces a printed image by selectively heating coated thermal paper when the paper passes over the thermal print head.

Scroll Down to Select Page 4 for the next topic – Lesson 3: Security and Ethics 


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