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ZyBooks 5 - Coggle Diagram

- - - - Access time
        
        time required to access the first byte in a read or write operation
      - Transfer rate
        
        speed at which data is read or written, following initial access.
    - - Volitile memory - lost when disconected
      - non-volatile - retained without power
  - - - primary memory used when computer operates
      - fast, expensive, limited capacity
    - - SSD
      - less expensive, higher capacity
      - faster reads than writes
  - - - Magnetic disk groups data in sectors.
        
        traditionally 512 bytes per sector but 4 kilobytes with newer disk formats
      - Flash memory groups data in pages
        
        usually between 2 kilobytes and 16 kilobytes per page
    - - database and files systems use a uniform size called a block
      - independent of storage media
      - storage data is managed by controllers, which convert between blocks and sectors or pages
      - the conversion is internal to the storage device, so the database is unaware of page and sector sizes
      - block size must be uniform within a database but, in most database systems, can be specified by the database administrator
      - usually supports 2 k to 64 k
        
        Smaller blocks are better for transactional applications, which access few rows per query.
        
        Larger block sizes are usually better for analytic applications, which access many rows per query.
  - - - when rows small, more fit in block. can read and write multiple blocks faster
      - less wasted storage - blocks fit together better
  - - - faster data access - more column values are transferred per block reducing time to access storage media