Computer Science OCR Topic 1 Memory and Storage

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  • Memory and storage
    • ROM
      • Contains the instructions that are set up by the manufacturer when the chip is created
        • This includes instructions for how to: start the computer, access the built-in hardware and load the operating system into RAM
        • This is permanent software and cannot be altered easily
      • Stored in a chip directly connected to the CPU through buses
      • Can be read from but cannot be written to (Read Only Memory)
      • Non-volatile
        • Contents are not lost when the power is switched off
    • RAM
      • Holds data and instructions which the computer is currently using
      • Volatile
        • Contents are lost when the power is switched off
      • Acts as a buffer to the secondary memory
      • If too many applications are open the computer slows down
        • It has to transfer some data back to secondary memory to cope with the large amount of data
    • Secondary Storage
      • Solid state storage
        • Stores data using circuit chips
        • Advantages
          • Durable
          • Fast
          • No moving parts
          • Quiet
        • Disadvantages
          • Expensive
          • Less data capacity per unit of money
        • Storage capacity: 512GB-4TB
      • Magnetic storage
        • Disk heads on mechanical arms read and write data
        • Advantages
          • Fast read-write speed
          • Cheap
          • Large storage capacity
        • Disadvantages
          • Lots of mechanical parts- not very portable
          • Can be affected by magnetic fields
          • Can be noisy
        • Storage capacity: 200GB to 1TB is common but can be larger
      • Optical storage
        • Laser beam passes over pits and lands, measures reflection
          • Pits represent 0 and lands represent 1
        • Advantages
          • Cheap
          • Portable
          • Small
        • Disadvantages
          • Not much storage capacity
          • Easily damaged
          • relatively slow
        • Storage capacity: 700MB to 8.5GB
    • Flash memory
      • Used for easy and fast information storage
      • Non-volatile
    • Virtual memory
      • An extension of RAM used when RAM is full
      • In the HDD (Hard Disk Drive)
      • Is slower because copying to a hard disk is harder than reading/ writing to RAM

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