• Floppy Disks
• Hard Disks
• Optical Disks
• Magnetic Tape

Storage Devices

Two types:

• Direct Access
• Sequential Access

Floppy Disks

Floppy disks are inexpensive removable direct access storage mediums that are used primarily to save and transport documents.  
 

A floppy disk need to be formatted before it can be used.  Formatting the disk involve preparing the tracks and sectors that are used to store the data.  

Four types of floppies are:

• 3½ inch HD disks
    80 tracks, 18 sectors per track, 1.44MB capacity
     
• Zip disks
    3065 tracks, 32 sectors per track, 100MB capacity
     
• SuperDisks
    120MB capacity
      
• HiFD disks
     200MB capacity

Hard Disks

Hard disks provide direct access to data stored on rigid metallic platters. They are much faster than floppies and provide much greater storage capacity.

Floppy, Hard disks, and Tape drives are magnetic storage devices that stores data by magnetizing magnetic particles on the disk.

Three types of hard disks are:

• Internal hard disks are also known as fixed disks because they are attached within the system unit.  They are typically enclosed with one or more metallic disks to protect against a head crash.
             
    
• Hard Disk Cartridges are removable disks making it possible to expand the storage capacity of  the computer system by using multiple cartridges.  Two well-known hard-disk cartridges are Jaz and SparQ.
             
    
• Hard-Disk Packs are removable disks that are used by mini and mainframe computers.  Disk packs consists of several palters and have storage capacities that exceeds those of the Internal and Cartridges types.
             
   

Optical Disks

While floppy and hard disks use magnetic charges to represents data, optical storage uses reflected light.  Optical disks are read by measuring the reflected light from a projected laser beam on the disk surface.  Flat areas on the disk surface, known by lands, are reflective while bumpy areas, known by pits, are non-reflective. The amount of reflected light is then used to determine weather the area represent a 1 or a 0.

Two types of optical disks exists:

• Compact Disk (CD)  can store up to 650MB of data.  The rotational speed of the drive determine how fast data can be read from the disk. For example a 24X drives can transfer data at 3.6MB per second, while a  36X drive can transfer data at 3.6MB per second.
   
  There are three types of CDs:
  • CD ROM
  • CD-R
  • CD-RW

      

• Digital Versatile Disk (DVD)  can store up to 9.4 GB of data with newer drives likely to have 17 GB capacities.  This give DVDs the ability to store seven to fourteen times more data than CDs.  
   
  In term of video, a CD can store only about an hour of fair quality video, a DVD on the other hand can store more that 2 hours of very high quality video making then ideal for movie storage.
   
  Like CDs there are three types of DVDs:
  • DVD ROM
  • DVD-R
  • DVD-RW

Magnetic Tapes

Magnetic tapes are removable sequential access mediums.  This make them slow when trying to access specific information since it will involve scanning the tape from beginning for the needed information.  Tapes however are very effective in backing up large amount of data.  Two types of tape mediums are Magnetic Tape Streamers and Magnetic Tape Reels.

• Magnetic Tape Streamers are used mostly to backup microcomputers data.  Typical tape capacities are 120 MB to 5 GB.  
             
     

• Magnetic Tape Reels these are used in mini and mainframe computers and can store much more data than the Magnetic Cartridges used by  microcomputers.
         

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