External hardware components and peripherals, cost, image and function.

Keyboard

The set of typewriter-like keys that enables you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. The keys on computer keyboards are often classified as follows:

·  alphanumeric keys -- letters and numbers

·  punctuation keys -- comma, period, semicolon, and so on.

·  special keys -- function keys, control keys, arrow keys, Caps Lock key, and so on.

The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first six keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing, is the Dvorak keyboard.

There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 keys. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys.

In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen.

There are several different types of keyboards for the Apple Macintosh. All of them are called ADB keyboards because they connect to the Apple Desktop bus (ADB). The two main varieties of Macintosh keyboards are the standard keyboard and the extended keyboard, which has 15 additionalspecial-function keys

Cost-$20

Mouse

 

The other most often used input device is the mouse. Once again they can some in all sorts of colours and various types of connectors. Most mice on a personal computer (PC) have two buttons, while the typical mouse on an Apple Mac has only one button.

The mouse operated simply on a small weighted ball that can move two rollers. One roller determines how much vertical movement, while the other determines the horizontal movement.

One extra feature on the mouse today, that is not traditional, is the scroll wheel. It can be used to scroll up and down a document. It can even operate as a third button.

The most common connector is a PS2, the same as the keyboard. This means it is possible to connect both the keyboard and mouse in the wrong sockets. This will not harm the computer but it will not function correctly.

As with the keyboard, it is possible to get other types of connectors such as USB (Universal Serial Bus), Infra-red and Wireless. We won’t be examining these in detail.

Cost-$29.99

Monitor

Monitors are display devices external to the computer case and connect via a cable to a port on the video card. Even though the monitor sits outside the main computer housing, it is an essential part of the complete system.

Monitors come in two major types - CRT and LCD. CRT monitors look much like traditional televisions and are very deep in size. LCD monitors are much thinner while still offering equivalent, if not better, graphics quality. LCD monitors are beginning to obsolete CRT monitors due to their smaller "footprint" on the desk and decreasing price.

Most monitors range in size from 15" to 21" or more. This size is a diagonal measurement from one corner of the screen to the other.

Cost-$170

Printers

In computers, a printer is a device that accepts text and graphic output from a computer and transfers the information to paper, usually to standard size sheets of paper. Printers are sometimes sold with computers, but more frequently are purchased separately. Printers vary in size, speed, sophistication, and cost. In general, more expensive printers are used for higher-resolution color printing.
Personal computer printers can be distinguished as impact or non-impact printers. Early impact printers worked something like an automatic typewriter, with a key striking an inked impression on paper for each printed character . The dot-matrix printer was a popular low-cost personal computer printer. It's an impact printer that strikes the paper a line at a time. The best-known non-impact printers are the inkjet printer, of which several makes of low-cost color printers are an example, and the laser printer . The inkjet sprays ink from an ink cartridge at very close range to the paper as it rolls by. The laser printer uses a laser beam reflected from a mirror to attract ink (called toner ) to selected paper areas as a sheet rolls over a drum.
The four printer qualities of most interest to most users are:

• Color: Color is important for users who need to print pages for presentations or maps and other pages where color is part of the information. Color printers can also be set to print only in black-and-white. Color printers are more expensive to operate since they use two ink cartridges (one color and one black ink) that need to be replaced after a certain number of pages. Users who don't have a specific need for color and who print a lot of pages will find a black-and-white printer cheaper to operate.
• Resolution: Printer resolution (the sharpness of text and images on paper) is usually measured in dots per inch ( dpi ). Most inexpensive printers provide sufficient resolution for most purposes at 600 dpi.
• Speed: If you do much printing, the speed of the printer becomes important. Inexpensive printers print only about 3 to 6 sheets per minute. Color printing is slower. More expensive printers are much faster.
• Memory: Most printers come with a small amount of memory (for example, one megabyte ) that can be expanded by the user. Having more than the minimum amount of memory is helpful and faster when printing out pages with large images or tables with lines around them (which the printer treats as a large image).

Cost-$150

Speakers

An electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance.

Cost-$15