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The memory System (Cache Memories (Memory Address (word (4 bits word is…

- - - - Direct mapping
      - Associative mapping
        
        More flexible
        
        Advantages
        
        Efficient
        
        Disadvantage
        
        Higher implementation complexity
      - Set-associate mapping
        
        Use combination of direct and associative mapping
        
        Advantages
        
        Reduce hardware implementation cost
        
        Remove contention problem
        
        Disadvantage?
  - - - 4 bits word is used to identify one of 16 words in the block
        
        Select the desired word from the line using the word bits.
    - - 7 bits block is used to identify one of 128 blocks in the cache
        
        Determine what block/line to look in – easy; just index into the cache using the block/line bits of the address.
    - - 5 bits tag is used to identify one of the 32 blocks in the main memory currently resides in the cache
        
        Compare the tag bits (leading 5 bits) of the address with the tag of the line. If it matches, the block is in the cache.
    - - Easy to implement
    - - Not very flexible
- - - - Each surface is divided into concentric tracks, each track is divided into sectors
      - Data bits are stored serially on each track
      - Data are preceded by a sector header, which contains ID to find the desired sector on the selected track
      - There are additional bits for ECC (error correcting code): used to detect and correct errors during writing/reading the data bytes
  - - - A laser beam is directed onto a spinning disk, with tiny indentation arranged to for a long spiral track on its surface
      - Indentation reflects the focused beam toward a photodetector, which detects the stored binary patterns
      - Bright spot: when light reflects solely from a pit or land, binary 0
      - Dark spot: no reflects from light detected by the photodetector, binary 1
- - - - which parts of virtual address space are in the physical memory
- - - - Advantage
        
        Very low power consumption
        
        Fast access time
      - Disadvantages
        
        Expensive
    - - No data when no power supply
      - Accessed frequently
      - DRAM Characteristics
        
        Charge in a capacitor
        
        reduce overtime
        
        refreshed periodically
      - Advantages
        
        less complex memory cells
        
        Higher density memory
      - Disadvantages
        
        Periodic refreshment
        
        Slow access time
      - DRAM Types
        
        (SDR) Single Data Rate, Synchronous DRAM
        
        (DDR) Synchronous Double Data Rate
        
        Asynchronous DRAM
- - - - manufacturing
      - written only once
    - - Load some data
      - Fuse
    - - Erased and new data to be written into it
      - Exposing to UV light
    - - Electrical erasable
      - Disadvantage : Different voltages
    - - Write an entire block
      - single power supply voltage