Instruction Formats: Instruction Length

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Length of instruction format affects and affected by

  • Memory size
  • Memory organization
  • Bus structure
  • CPU complexity
  • CPU speed

Trade off is between desire for a powerful instruction repertoire and a need to save space.

Instruction length should be equal to memory-transfer length or one should be a multiple of other. Otherwise, we will not get an integral number of instructions during a fetch cycle.