Magnetic disks

A main problem with any recording tape is the fact that data is strewn out along a highway. To get from one bit of information to some other bit, it may be necessary to traverse entire length of highway. The distance can be even hundreds of feet.But on the magnetic disk, no 2 bits of data are, in practice, ever separated by the distance greater than diameter of disk. Because of this, disks are faster than the tapes for data storage and retrieval. Magnetic disks are popular for the digital data. They are not often used in analog applications, although R & D continues in quest for a high-resolution, reliable, magnetic video disk.Personal and commercial computers always use magnetic disks.They come in 2 forms:

- Hard disk and floppy disk

- diskette.

The hard disk in a characteristic PC can hold several gigabytes of the data. This figure doubles every few years, and trend can be expected to continue until point of diminishing returns is reached. Hard disks are installed permanently in the computer. You cannot take out and replace a hard disk. Complex software—specifically the kind involving graphics, video games and simulations, and complex mathematics—needs a lot of memory space, and as software itself becomes more sophisticated, consumer demand will follow along with it. Therefore, you might see, before too long, a hard disk with tera- bytes (TB) of capacity. A terabyte is around 106 MB.

Floppy disks and diskettes are interchanged in seconds, so there is no limit to how much data you can sock away on them. A full-wall bookcase of floppies could have more manuscript than you would write in 1,000,000 years. A typical PC floppy disk comes in the flexible, square package measuring 5-1/4 × 5-1/4 inches and is around 1 mm thick. These disks have 1.2 Mb of capacity. Larger floppies are used in commercial computers. A smaller diskette is in the rigid, square package measuring 3-1/2 × 3-1/2 inches and is a bit thicker than the floppy package. It holds a little more data than the physically larger floppy cousin: 1.44 Mb.It probably will not be long before the memory capacities of floppy disks and diskettes increase, so do not take these figures seriously.