Lesson 2. Magnetic storage

I. Read and translate the text.

Magnetic storage devices store data by magnetizing particles on a disk or tape. There are basically three types of magnetic storage devices available to the computer user — 3.5″floppy drives and diskettes, hard drives and tapes.

A floppy disk is so called because it consists of a flexible sheet of plastic, coated with iron oxide — a magnetizable material. A floppy disk drive spins at 360 revolutions per minute (rpm), so it’s relatively slow. However, a hard drive spins at over 7,200rpm and stores data on a stack of metal rotating disks called platters. This means you can store much more data and retrieve information much faster.

New disks need to be formatted though as a rule they come preformatted from the manufacturer. The operating system (OS) organizes the disk surface into circular tracks and divides each track into sectors. The OS creates a directory which will record the specific location of files. When you save a file, the OS moves the read/ write head of the drive towards empty sectors, records the data and writes an entry for the directory. Later on, when you open that file, the OS looks for its entry in the directory, moves the read/ write heads to the correct sector and reads the file in the RAM area.

The OS allows you to create one or more partitions on the hard drive, in effect dividing it into several logical parts. Partitions allow installing more than one OS on the computer. The user can also split the hard drive to store the OS and programs on one partition (this is the internal hard drive usually called C: drive) and data files on another so that when a problem occurs the OS may be reinstalled without affecting the data partition.

External hard drives are connected to the USB or FireWire port of the computer. They can be as small as a wallet but can have as much capacity as internal drives; they are usually used for backup or as secondary storage.

Hard drives are very sensitive to vibration and shocks, especially when they are operating.

A tape drive reads and writes data on tapes. It is sequential-access — i.e. to get to a particular point on the tape, it must go through all the preceding points. Tapes are used for data collection, backup and archiving.

The average time required for the read/ write heads to move and find data is called seek time (or access time) and is measured in milliseconds. Seek time shouldn’t be confused with transfer rate — the average speed required to transmit data from the disk to the CPU, measured in megabytes per second.

II. Decide whether these sentences are true or false. Correct the false ones.

1. A hard drive spins at the same speed as a floppy disk drive. 2. If you format a hard drive that has files on it, the files will be deleted. 3. Hard drives cannot be partitioned to run separate operating systems on the small disk. 4. Seek time and transfer rate mean the same thing. 5. Disk drives are not shock resistant, especially in operating mode.

III. Read each paragraph carefully and say briefly what they are about.

IV. Speak on advantages and disadvantages of magnetic storage devices.

V. Read the text and translate it into Russian. Write a short summary of it.

The function of the memory unit is to store programs and data. This function can be accomplished with a variety of equipment. It is useful to distinguish between two classes of memory devices which comprise the prime and secondary storage. Primary storage, or the main memory, is a fast memory capable of operating at electronic speeds, where programs and data are stored during their execution. The main memory contains a large number of semiconductor storage cells, each capable of storing one bit of information. These cells are rarely read or written аs individual cells. Instead, they are processed in groups of fixed size called words. The main memory is organized so that the contents of one word, containing n bits, can be stored or retrievedin one basic operation.

To provide easy access to any word in the main memory, it is useful to associate a distinct name with each word location. These names are numbers that identify successive locations, which are hence called address. A given word is accessed by specifying its address and issuing a control command that starts the storage or retrieval process.

The number of bits in each word is often referred to as the word length of the given computer. Large computers usually have 32 or more bits in a word, while microcomputer and minicomputer word lengths range from 8 to 32 bits. Small machines may have only a few thousand words, large machines often have millions of words. Data is usually manipulated within a machine in units of words, multiples of words, or submultiples of words. A typical access to the main memory results in one word of data being read from the memory or written into it.

Notes

Can be stored or retrieved – зд. могут быть найдены; successive locations – последовательные ячейки. Data is usually manipulated – С данными обычно работают.