Technical details

Date: 2015-10-07; view: 974.

Floppy disks are so called because they consist of flexible, plastic material which has a magnetizable surface.

The surface of a disk is divided into concentric circles or 'tracks', which are then divided into 'sectors'. When you insert a blank disk into a disk drive, it must be 'initialized', or formatted, before information can be recorded onto it. This means that magnetic areas are created for each track and sector, along with a catalogue or 'directory' which will record the specific location of files.

When you save a file, the operating system moves the read/write heads of the disk 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 sectors, and reads the file into the RAM area.

Hard disks work in the same way as floppies. But they have important advantages: they can hold much more data and spin at higher speed, so you can store and retrieve information much faster than with floppies. The speed at which a hard drive finds data is called 'access time' – or seek time. The average access time is measured in milliseconds (ms). Most hard drives have an access time of 8 to 14 ms.

You have to distinguish between access time 30 (e.g. 9 ms) and 'data transfer rate' (the average speed required to transmit data from a disk system to the RAM, e.g. at 10 megabits per second). Remember that the transfer rate depends also on the power of your PC.

If you only use word-processing programs, you will need less storage capacity than if you use CAD, sound and animation programs. If you need an extra hard drive, you should consider the type of mechanism. There are 'internal' and 'external' drives which are both rigid disks sealed into the drive unit, either within or attached to the computer.

Another type of hard drive, known as 'removable', allows you to record data on 'cartridges', which can be removed and stored off-line for security purposes. Some systems allow you to back up your entire PC on one disk.

Laptops use pocket-sized drives. Digital cameras and music players use microdrives be with special cards.

A floppy disk drive spins at 360 revolutions per minute. A hard disk drive spins at 7,200 rpm and stores data on a stack of metal rotating disks, called platters.

CNow read these sentences and decide if they are true (T) or false (F).

1 Hard drives are faster than floppy drives.

2 'Access time' refers to the average time required for the recording heads to move and access data.

3 'Access time' and 'data transfer rate' mean the same.

4 Hard disks use rigid rotating disks.

5 A hard drive is about 20 times faster than a floppy disk drive.

6 If you use multimedia applications you need the same storage capacity as required for word processors.

7 Removable cartridges are not transportable.

Exercise 4.World building

Look at the groups of words and decide what class each word belongs to: noun, verb, adjective or adverb. Complete the sentences.

1 _____ is the science of magnetic phenomena and properties.

2 Floppy and hard disks are considered as ______ storage devices.

3 Data is recorded on a disk in the form of _____ spots called bits.

4 All disks must be initialized before information can be _____ onto them.

5 The ______ heads follow the tracks and magnetize the coating along each track.

6 A disk drive works very much like a tape _____ that can both play and record.

7 After you create, delete and modify a lot of files, the hard disk becomes _____, with bits and pieces spread all over the disk.

8 _____ slows down the speed at which data is accessed because the disk drive has to work harder to find the parts of a file stored in many different locations.

9 To reorganize your hard disk, you can use a disk optimizer or _____: this will reorder your files into contiguous clusters.

In a fragmented disk, a file is stored in non-contiguous sectors	In a defragmented disk a file is stored in neighbouring sectors