Secondary Storage

  • Created by: dtomkins
  • Created on: 25-04-18 17:30
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  • Secondary Storage
    • Magnetic devices
      • The magnetic hard disk uses a stack of magnetised rigid plates that rotate.
        • The heads hover over the surface and can move in and out across the platters to read data.
        • The magnetic disk drive was first invented by IBM in 1956. It had a stack of 50 platters, was the size of a fridge, was able to store around 5Mb of data and cost $50,000
      • The use of magnetic media goes back to 1989
      • The magnetic disk drive is a reliable and cost-effective storage solution, providing high capacity at low cost
        • IT is used in most personal desktop and laptop computers as well as in large commercial systems, where several large disks are combined to provide large data storage facilities.
        • There are also portable versions of the magnetic disk drive that can be used as external devices to transfer large amounts of data or to act as a backup for important data
    • Optical disks (CD)
      • This was invented in the mid-1980's
      • Read by using laser light
        • A sensor detects the reflections from the surface when a laser light is hone onto them
      • There are two forms: Read and write / read only
        • READ ONLY these are written to once at the manufacturing stage and are used to distribute programs, video or data that is read only
        • READ/WRITE can be used as secondary storage to back up data or to safely transfer data between computers.
    • Flash memory
      • It is a very common form of personal portable fil storage and is often used as a USB device to transfer data between computers, in cameras to store images and in table computers and other portable devices as the main form of storage
      • Many laptop computers are now using large solid-state drives as an alternative to magnetic disk drives
      • SSD
        • Lower latency times
        • no moving parts so they are low power devices that do not generate heat or noise.
        • Data being fragmented is not an issue
        • Significantly lighter than magnetic disk drives
        • Not easily broken
    • Choice of secondary storage
      • Capacity: How much data does it need to hold?
      • Speed: How quickly can the data be transferred and read?
      • Portability: Does the data storage device need to be transported?
      • Durability: How robust is the medium?
      • Reliability: Does it need to be able to be used over and over again without failing?
  • We can estimate the size of a file from its contents but the formatting can add considerably to the size


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