Instruction sets

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Steps involved in instruction execution in CPU
  • Instructions and data are the information fed to a computer. Instructions are explicit commands that
    • Govern the transfer of information within a computer as well as between the computer and its I/O devices.
    • Specify the arithmetic and logic operations to be performed.
  • A set of instructions that perform a task is called a program usually a program is stored in the memory.
  • The processor then fetches the instructions comprising the program from memory one at a time and perform the desired operations.
  • The computer is under control of stored program, except for the possibility of external interruption from the operator or by I/O devices connected to the machine.
  • The operation of the CPU is determined by the instructions it executes.
  • These instructions are referred to as machine instructions or computer instructions.
  • The collection of different instructions that the CPU can execute is referred to as the CPU‟s instruction set.
  • Each instruction may contain the information required by the CPU for execution.
    • Operation Code: Specifies the operation to be performed. The operation is specified by a binary code known as the operation code or opcode.
    • Source Operand Reference: The operation may involve one or more source operands, that is operands that are inputs for the operation
    • Result Operand Reference:  The operation may produce a result.
    • Next Instruction Reference:  This tells the CPU where to fetch the next instruction after the execution of this instruction is complete

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