Computer System Architecture - Microprogrammed Control

16. Consider the instruction set architecture of a general-purpose machine. Suppose that a total of 20 control signals are present, out of which 7 are mutually exclusive while the rest are not. The number of bits required in the control word (for microprogramming) will beat least .................... .

  • Option : A
  • Explanation : The 7 mutually exclusive signals can be encoded in ceiling(log2 7) = 3 bits,
    while the remaining 13 signals will remain un-encoded. So the number of
    bits in a control word will be 3 + 13 = 16.
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17. Suppose an instruction set architecture of a general-purpose machine has a total of 126 control signals. The number of bits required in control word for horizontal and vertical micro-instruction encoding are:

  • Option : A
  • Explanation : For horizontal encoding, one bit is used for each control signal; therefore, we shall require 126 control signals.
    For vertical encoding, the 126 control signals can be encoded in ceiling(log2 126) = 7 bits.
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18. Which of the following is true for MIPS32 register bank?

  • Option : C
  • Explanation : In MIPS32 architecture, two register operands are prefetched during the ID stage, which required two read ports in the register bank. Also, for pipelined implementation, a register write can occur during WB. Thus two read and one write ports are required in the register bank.
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19. Which of the following is true for the ID(Instruction Decode) stage of the MIPS32 data path?

  • Option : A
  • Explanation : Option A and B both are correct.
    For the MIPS32 instruction execution, the instruction is decoded and the register operands are pre-fetched during ID stage.
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