ISA & Assembly

Which statement is correct about two CPUs that implement the same instruction set architecture (ISA)?

  1. AThey are built with the same circuits, so their performance and power are the same
  2. BEven if their internal circuits differ, they can run the same machine-code program
  3. CThey must be made in the same fab using the same process
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Answer: B. Even if their internal circuits differ, they can run the same machine-code program

An ISA is the contract between software and hardware that defines the kinds of instructions, their bit layout, the number of registers and so on. The internal organization, such as the number of pipeline stages, the cache sizes and the branch predictor, is called the microarchitecture and is chosen separately from the ISA. So one ISA can have both small low-power cores and large high-performance cores that differ in speed and power yet run the same machine code. The fab and process have nothing to do with the ISA.

  • A. The circuit organization (microarchitecture) differs between products.
  • B. Correct. The ISA is a contract; the implementation is free.
  • C. An ISA says nothing about how chips are manufactured.
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More ISA & Assembly questions

  1. What is a characteristic of a load-store architecture such as RISC-V?
  2. What is the property of register x0 (zero) in RISC-V?
  3. Which describes the general-purpose integer registers of RISC-V RV32I (the 32-bit base integer instruction set)?
  4. What is the relationship between assembly language and machine code?
  5. Which real instruction does the assembler use for the RISC-V pseudo-instruction "nop" (do nothing)?