Compact Discs

A new type of discs – digital videodisc (DVD) – was developed by Philips and Sony in 1995. It looks and works like a CD-ROM but can store more than 15 times as much information. Single-sided disc² can store up to 4.7 gigabytes of data such as high-definition digital video files. A DVD has the same dimensions as a standard CD but cannot be read by a standard CD player, though a DVD player can read standard CDs. Beginning in the late 1990s, various writable and rewritable DVD formats were introduced.

Flash memory is another electronic storage unit. Since its invention in the late 1980s (by Intel and Toshiba), it has become standard for portable devices such as digital cameras, cellular telephones, PDAs, MP3 players, and video-game machines. In the early 21st century, flash memory devices that could fit on a key ring and had storage capacities of up to 1 GB (and later more) began to serve as portable hard drives.

(3) Input Devices

Input hardware consists of external devices – i.e. components outside of the computer's CPU – that are used to enter information and instructions into a computer for storage or processing. The purpose of an input device is to convert incoming data into binary code (i.e. combinations of 0s and 1s) understandable to a digital computer. The most common input devices are a keyboard and a mouse.

A keyboard is a device with buttons or keys that a user presses to enter text, commands, numbers, or other data into a computer. The most used English-language keyboard is called QWERTY. (It was created by an American inventor and printer Christopher Sholes in the late 1860s.) QWERTY is not a word. It is the first six letters in the top alphabet row on a keyboard. That combination of letters is often used to name the standard keyboard in contrast to other keyboards. The minimum number of keys on a board is 44 but modern keyboards may have more than 100 buttons.

A mouse is a mechanical or optical hand-held device. It has two/three buttons and a sсroll wheel on the top as well as a rolling ball or an optical sensor in its base. To move the cursor on the display screen, the user moves the mouse around on a flat surface. When the cursor reaches the required location, the user presses the right or left button on the mouse once or twice. Clicking the button, the user can select operations, activate commands, create or change images on the screen.

A trackball, joystick, light pen, and laser scanner also refer to input devices.

A trackball is an inverted mouse. (See Figure 5)The only functional difference between a mechanical mouse and a trackball is in how the ball is moved. With a mouse, the ball is rolled by moving the whole unit over a desktop or other surface. With a trackball, the user rotates the ball itself while the unit is stationary. One of the main advantages of a trackball is that it takes little desktop surface. Figure 5