23. What is an Optical Drive? Give its brief characteristics.

An optical drive is a piece of equipment that uses a laser to read or write information on a disc. Optical drives are often associated with computers, but they can stand alone as appliances. For instance, a Digital Versatile Disc (DVD) player, Blu-ray disc (BD) player, and Compact Disc (CD) players are considered optical drives even though they may not be in a computer system. Many video games also use an optical drive to read the game’s disc. Despite what type of disc they read or write, all these applications have the same basic workings.

The optical path makes an optical drive work. The optical path is composed of three components: a laser, a lens, and a photodiode. The laser writes and reads the data. The lens guides the laser across the surface of the disc. Lastly, the photodiode detects light reflected off the disc’s surface. The optical drive also uses two servomechanisms, or servos — one to maintain the proper distance between the disc and laser and the other to make sure the laser is moving in a continuous spiral path.

Blu-ray (known also a Blu-ray Disc and BD) is a next-generation, massive optical storage medium. The disc measures the same as a regular Digital Versatile Disc (DVD) or Compact Disc (CD) (4.7 inches/120 mm in diameter), but the Blu-ray Disc format is of a far greater capacity than these two predecessors and is used particularly in the field of high-definition (HD) media. The disc takes its name from the violet or blue colored laser with which data is read and written. It is owing to the very short wave length of this laser that the Blu-ray format can store massive amounts of data. With a laser beam of just 405 nanometers, a single layer Blu-ray Disc has a maximum storage capacity of 25 gigabytes while a dual layer disc has a maximum storage capacity of 50 gigabytes.

A digital versatile disc, which many people refer to by its acronym "DVD," is a plastic disc usually 4.7 inches (12 cm) in diameter that uses microscopic pits on the surface of the disc to store information. An aluminum coating covers the pits so that a thin laser can read the information. They can contain anywhere from 4.7 to 17.0 gigabytes of data. Due to their large storage capacity, digital versatile discs are popular for data storage and are also a common medium for the storage and distribution of video, especially movies.

Since 1982, consumers have had access to one of the great breakthroughs in media storage technology: a slim, round, and shiny object known as the compact disc (CD). Also known as an optical disk, the 4.724 inch (120 mm) round polycarbonate CD has largely replaced less reliable but similar formats like the cassette tape and vinyl record as a unit for digitally stored audio. Despite its size, one standard compact disc may hold up to 80 minutes of music. It remains the most preferred and popular medium for audio recordings. The CD-ROM, a later version of the same technology, holds up to 700 megabytes (MB) of data and is widely used by individuals and businesses for archiving important documents, photographs, and software.

24. What are computer peripherals? Give examples of external and internal devices.

This article is about a computer device. For the Greek subdivision, see Peripheral units of Greece. For the mathematical term, see Boundary parallel.

A peripheral is a device attached to a host computer, but not part of it, and is more or less dependent on the host. It expands the host's capabilities, but does not form part of the core computer architecture.

Examples are computer printers, image scanners, tape drives, microphones, loudspeakers, webcams, and digital cameras.

25. What is the difference between an input and an output device? Give examples.

Input devices and output devices are computer hardware that enable an operator to interact with the computer. Without input devices, a computer user would not be able to feed instructions to, or send and store information in, a computer; without output devices, the computer would not be able to give processed information back to the user.

Input devices give data and instructions to the computer e.g,mouse,keyboard

output devices get information from the computer e.g,monitor

Accessibility

Accessibility is a point of difference between input and output devices. An input device is used to take instructions from a user and give it to the computer and therefore has to be easily accessible to the user. If the mouse, instead of being on top of the table, was inside the computer's tower casing, it would be cumbersome (and dangerous) to operate the device. Output devices, on the other hand, do not rely on any form of physical contact with the computer user and may be present as an internal component. Examples are the expansion cards (sound and video) that are fitted into slots in the motherboard

Name Type of Device Use:

Keyboard Input To type information

mouse input To select objects

Monitor output To see information

26. What text manipulation functions can word processing provide?

27. How does a web page work?

Web pages, such as the one you are now reading, "live" on web servers all over the Internet. Those pages are written in HTML (HyperText Markup Language), a simple language that allows us to create hypertext links from one page to another. Designers put the content of the page (the text of the page) in the HTML file, and usually determine what the page will look like with a separate "style sheet" file. Style sheets are written in a language called CSS (Cascading Style Sheets).

Web browsers, such as the program you are using right now on your computer to see this web page, speak to web servers in a language (a "protocol") called HTTP (HyperText Transfer Protocol).

But before the web browser can talk to the web server, it needs to know the web server's IP address on the Internet - just as you have to know your friend's phone number before you can call him. So how do web browsers translate a friendly name like www.google.com into an IP address? By talking to a DNS (Domain Name Service) server.

Once the web browser knows the IP address of the server, it can make an HTTP protocol connection and ask for the page you want to see.