III. Read and translate the following text.

Types of storage devices

The storage device is one of the most important parts of any computer system. The principal component of it is the memory which can be divided into two types: primary and secondary. The primary memory is volatile (or erasable) and the secondary memory is non-volatile (it means that the contents cannot be erased). Storage devices are used to hold and process information. Electronic data storage requires electrical power to store and retrieve data. Typically, data can be stored in either analog or digital format on different types of media. Most data storage media are considered to be permanent (non-volatile) storage, that is, the data will remain stored when power is turned off.

The compact cassette, often referred to as an audio cassette or simply tape, is a magnetic tape sound recording format. This type of media was used for audio home recording and data storage of early microcomputers. Cassette is a French word meaning «little box». Compact cassettes consist of two small spools and a magnetically coated plastic tape. These spools and their attendant parts are held inside a protective plastic case.

The hard disk drives are the example of secondary memory devices. They are available in different configurations and with various access speed, i.e., how fast the data can be accessed from the hard disk drive. Each side of platter of the hard disk drive has a read/write head that is used to retrieve or store data. The surface of the platter is coated with magnetic material. The read/write head reads the data from the surface by interpreting the variations in the magnetic field. The platters are mounted on a fixed spindle which rotates at the speed of about 7200 revolutions per minute (rpm). The read/write heads move horizontally across the platters from the edge to the center so that they can read or write data to any part of the surface. Hard disk drives that are available now have the capacity ranging from 40 gigabytes to several terabytes (1 terabyte is equal to 1, 000 gigabytes).

A compact disk (originally developed for storing digital audio) is an optical disk used to store digital data. The CDs have been available on the market since October 1982. They remain physical media for sale of commercial audio recordings up to present days. Standard CDs have a diameter of 120 mm and can hold up to 80 minutes of audio (700 MB of data). The Mini CD has various diameters ranging from 60 to 80 mm and they are sometimes used for device drivers. The technology was later adopted and expanded to include data storage CD-ROM, write-once audio and data storage CD-R, rewritable media CD-RW, Super Audio CD (SACD), Video Compact Disks (VCD), Super Video Compact Disks (SVCD), PhotoCD, PictureCD and Enhanced CD. CD-ROMs and CD-Rs remain widely used technologies in the computer industry. By 2011, 750 billion CDs have been sold all over the world.

A digital versatile disk, also known as a digital video disk, is an optical disk storage media format which is used to store video and data. DVDs have the same dimensions as compact disks (CDs) but they are able to store much more data. The variations of the term DVD often describe the way data is stored on the disks: DVD-ROM holds data that can only be read but not written, DVD-R and DVD+R can record data only once and then they can be used only as DVD-ROMs. DVD-RW, DVD+RW and DVD-RAM can both record and erase data many times. The wavelength used by standard DVD lasers is 650 nm. DVD-Video and DVD-Audio disks refer to properly formatted and structured video and audio content respectively. Other types of DVDs, including those with video content, may be referred to as DVD-Data disks.

Blu-ray Disks, as the next generation of high quality optical formats, have the same features (physical size, operation principle) as DVDs and CDs. Blu-Ray was invented by Grahmbo Huysmans and developed by the Blu-ray Disk Association (a group representing consumer electronics and computer hardware manufactures). The name «Blu-ray Disk» is derived from the blue laser (violet-coloured) used to read and write onto this type of disk. Because of the wavelength (405 nanometers), much more data can be stored on a Blu-ray Disk than on DVD disk, which uses red (650 nm) laser. A dual-layer Blu-ray Disk can store more than 50 GB of data. On February 19, 2008, Toshiba, the main company supporting HD DVD, announced that it would not develop and manufacture HD DVD players and recorders.

IV. Answer the following questions:

1. What storage devices are mentioned in the text?

2. How many CDs have been sold by 2011?

3. What types of optical disks do you know?

4. Who was Blu-Ray invented by?

5. What is the capacity of dual-layer Blu-ray disk?

6. What does thecompact cassette consist of?

7. What is the way of recording data on the magnetic tape?

8. What is the wavelength of a DVD disk laser?