10 Magnetic tape is a long plastic strip coated with a magnetic substance such as iron oxide, which works on the same principles as those that operate when you use a cassette tape in your walkman. Information can be written to the tape by the read/write head of a tape drive, and then stored as magnetised spots on the tape's surface. These spots can then be read by the same read/write head of the tape drive, converted to information that the computer can understand and sent to the CPU. Three types of tape are used:
· reel-to-reel tape
· cassette tape
· cartridge tape
11 A typical reel-to-reel tape is about 800m long, 1 cm wide and contained on a reel about 30 cm in diameter. These tapes can hold large amounts of information and are used with the larger computer systems.
12 Cassette tape is the familiar tape that we have all used and is about j 8 mm wide, comes in various lengths and is contained inside a plastic case. The early microcomputers used cassette tapes for backing store.
13 A cartridge looks like a large cassette but with wider and longer tape. Cartridge tapes are used both by large computer systems and microcomputers. A typical use with a microcomputer would be to create a copy of valuable information as a safety measure in case it were lost from its normal media storage. This procedure is known as backing up and should be done regularly in all computer systems.
14 Magnetic tapes suffer from one disadvantage: information is stored on them sequentially-one piece of information following another, so if a particular piece of information that is required is stored at the far end of the tape, the tape drive has to wind all the way through the tape before the required information can be read. This slows down the process of information retrieval, but this disadvantage has been overcome by the introduction of magnetic disks.
Tapes were used to store information long before the advent of computers, for example with ticker-tape and dictaphone machines.
15 A magnetic disk is a circular sheet of plastic coated with the same magnetic material as the magnetic tape. Its advantages over other forms of secondary storage are:
· access of information;
· speed of information transfer;
· amount of information stored.
16 Information is contained on the disk surface in a series of concentric, circular tracks. The read/write head can move backwards and forwards along the radius of the disk, thereby making it possible to access information directly.
17 Because the disk can spin at a much faster rate than a tape can move past the tape reader's read/write head, information stored on a disk can be accessed at a much faster rate.
18 The speed at which the disk rotates also permits information to be more densely packed onto the disk surface. In this way a disk can hold far more information than a tape.
Find out how much information the disks that you use with your computer can store.
There are three different types of disk.
· Floppy Diskettes
· Hard Disks
· Disk Packs
19 A floppy diskette is either 8,
5.25 or 3.5 inches in diameter and is contained inside a stiff plastk jacket.
It may be single sided-information only being stored on one side-or double
sided in which case both sides can be used. The magnetic material on the disk
surface may be
single, double or х4 density. The denset the material, the more information can be stored on the disk. A floppy diskette is used with a disk drive into which the diskette is inserted. The disk drive may have one or two read/write heads. A two headed disk drive is capable of
reading from and writing to both sides of the diskette without having toextract the diskette and turn it over. Floppy diskettes are standard means of storing information for use with a microcomputer.
20 A hard disk is made from aluminium instead of plastic and because of its rigidity can store more closely packed information than a floppy diskette. It can also be rotated at a much faster rate than a floppy diskette, thereby permitting an even faster rate of information access. Hard disks come in a variety of forms.
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