Secondary Storage

Secondary Storage

1. why is it needed ?

   • it stores data on the computer even when the power is off it is known as non volatile memory
   • it's different to primary storage which can stores data on RAM but only while there is power connected
   • when a computer is running the data is copied from secondary storage onto RAM which is why sometimes the loading sign comes up when the computer is shutting the changes made to the data are then copied back into secondary storage
   • - its much slower to access data from secondary storage than on RAM - data in secondary storage is permanent -Secondary storage typically has a far higher storage capacity than RAM

2. examples of secondary storage

   • magnetic drives
     • they have a tape or a disk surface which can magnetised with a pattern of north and south areas to represent the binary data. As the changing magnetic surface moves past a read head it reads the alternating pattern of tiny current changes as binary digits.
       • disavantages
         • Not reliable as they are easily physically damaged if unprotected and magnetic fields can damage the data.
         • Very slow to access data because floppy discs rotate far more slowly than hard discs and only start spinning when requested.
     • theses include
       • hard drives
       • floppy disks
       • magnetic tape
     • advantages
       • They are very cheap to buy
       • Data can be read directly from any part of the disk (random access)
   • optical devices
     • These use a circular disk surface where a spiral pattern of reflective and non-reflective areas represents the binary data as the disk surface moves past it.. A low-power laser beam tracks this spiral pattern and reflects laser light onto a light detector. The pattern of bright and non-bright reflections form a pattern which is read as binary digits.
     • these include
       • CD
       • DVD
       • blu-ray disks
     • advantages
       • relatively high capacity
       • portable and fast
     • disadvantages
       • quite expensive
       • not very robust

3. solid state devices

   • These store the binary data on semi-conductor material where a pattern of on/off semi-conductor switches represents the binary data.

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