Are where large amounts of info are stored, even when the power is off. The data on disks is stored as regions of changing magnetism on hard and floppy disks and as pits in plastic for CD ROMs. Special "heads" "fly" just above the surface of the rapidly spinning disks to read the data.


a)    Floppy Disks come in a 3.5 inch size, and can store anywhere from 360 KB to 1.44 MB. Info can be written to and read from floppy disks. Their advantage is that they can be removed from the computer and the data taken to another machine. Their disadvantage is that they don't hold very much info. The name comes from the flexible disk of magnetic particle-coated plastic inside the outside protective cover.


Figure 3.5Ē Floppy Disk


b)    Hard disks are not removable like floppies, but hold more info. Typical hard disks are available in capacities that range from 6-80 GB (Gigabytes) of data. They have read and write capability. Their name comes from the rigid (for more accurate positional alignment) magnetic-particle coated disk inside the protective case.


Figure 6. Hard Disk


c)     ZIP Disks.Zip disks are either external or internal drives that have capacity that ranges from 100 Megabytes to 250 Megabytes.The drives are the size of 3.5 inch disk but are thicker in size.


d)    CD-ROMs and CD-RW. This Compact Disk (CD), disk drive comes in either Read Only Memory (ROM) or Recordable and Rewritable (RW) format. It is a useful medium especially for huge databases or video/audio data. A CD ROM holds about 650 MB of data and is removable. The heads use lasers to read the pits in the plastic disks.The CR-RW is able to read and write information.CD-RW drives are able to write to recordable CD-R (Compact Disc Recordable) and/or CD-W (compact Disc Rewritable).This is a very convenient format since most computers have CD drives available to them.


Figure 6. Compact Disk with External CD-ROM Drive

e)    ZIP Disks


f)      DVD ROMs. Digital Versatile Disc (DVD)-Read Only Memory (ROM).This disk is similar to a CD with the exception that it is able to hold significantly more information.The capacity for storage for DVDís versus CD is between 4.38 GB and 15.9 GB of storage for a DVD to 650 MB for a CD.


g)    Disk controller is an electronic board in the computer that controls the disk. It tells the disk where to put the heads and what to do (read vs. write).