Home Computer: Hard facts on floppy disks

The hard disk is in fact a collection of disks, which superficially looks similar to a set of high quality and very fine vinyl records spaced out on a spindle. The disk spins at high speed when the machine is on and information is 'written' on to its various surfaces in much the same way that a tape recorder imprints electronic information on a tape - and, as many have found to their cost, erases information the same way, writes Nigel Willmott.

The hard disk can store large volumes of information, usually measured in megabytes - millions of bytes, or in text terms, millions of characters.

The trouble with the hard disk is that it is only as portable as the computer in which it is incorporated. 'Floppy disks' hold less information but can be taken out of the machine and stored and carried about separately. Using them is like putting a tape into a cassette recorder - which the first personal computers used to store information.

Floppy disks come in two physical sizes. The larger 5.25-inch disk, rather like an old-fashioned single record, is bendable - though doing so may result in the loss of the treasured first novel. The now more common 3.5-inch disks have a rigid outer protective cover, so are floppy in name only.

Both types of disk are simply pushed into the slot in the floppy disk drive. The 5.25-inch disk drives have a little handle to push into position to start the drive, the 3.5 disks automatically click into place, but have an eject button to take them out again.

Standard floppy disks usually store about 720,000 bytes - or 720 kilobytes (K) - on a PC, slightly more or less on other types of machine. High density disks store about 1.4 megabytes on a PC.

Blank disks can usually be used on any type of computer, if they are the right capacity for the disk drive - some do not read high density disks. The computer system has to 'format' a disk to its way of storing information before it can be used on a particular type of machine.