Control Unit Design: Hardwired vs Microprogrammed Quiz Quiz

Explore the key differences, advantages, and operational principles of hardwired and microprogrammed control units in computer architecture with this focused quiz. Enhance your understanding of how each control unit impacts processor performance, flexibility, and instruction execution.

1. Basic Characteristics

   Which statement best describes a primary characteristic of a hardwired control unit compared to a microprogrammed control unit?

   1. A hardwired control unit executes instructions using combinational logic circuits.
   2. A hardwired control unit is easier to modify for complex instruction sets.
   3. A hardwired control unit decodes instructions using firmware routines.
   4. A hardwired control unit uses control memory to store microinstructions.

   Explanation: A hardwired control unit relies on fixed combinational logic for instruction execution, leading to fast operation. In contrast, a microprogrammed control unit employs control memory to store microinstructions, not hardwired units. Modifying hardwired units is typically difficult, making them less adaptable to new instruction sets. Decoding via firmware routines refers to microprogrammed control, not hardwired operation.

2. Speed and Performance

   In a scenario where maximum execution speed is necessary, which control unit design is generally preferred and why?

   1. Microprogrammed control unit, thanks to parallel execution
   2. Microprogrammed control unit, for faster microinstruction fetching
   3. Hardwired control unit, due to its fast signal propagation
   4. Hardwired control unit, because it has more memory

   Explanation: Hardwired control units are faster because their logic is implemented directly with circuits, ensuring quick response. Microprogrammed units typically have an extra step of fetching and interpreting microinstructions, making them slower. While microprogrammed units can sometimes use parallelism, hardwired units are still known for speed. The amount of memory is not a significant factor in this context.

3. Flexibility and Modifiability

   If a processor designer wants to easily add new instructions or update existing ones, which control unit type is typically more suitable?

   1. Hardwired control unit, by altering wires and gates rapidly
   2. Microprogrammed control unit, by rewiring combinational circuits
   3. Microprogrammed control unit, as changes only require updating microcode
   4. Hardwired control unit, since it can be programmed directly

   Explanation: Microprogrammed control units can be updated by changing the microprogram in control memory, making modifications and enhancements relatively easy. Hardwired units require physical changes to circuitry, which is complex and time-consuming, not rapid. Hardwired units cannot be directly programmed like software. Rewiring combinational circuits applies to hardwired units, not microprogrammed ones.

4. Cost and Complexity

   Which factor makes microprogrammed control units more attractive for implementing complex instruction set computers (CISC)?

   1. Their immediate response time without decoding steps
   2. Their simpler modification process for new instructions
   3. Their exclusive use of analog components
   4. Their reliance on basic combinational logic only

   Explanation: Microprogrammed control units allow designers to implement and change complex instruction sets efficiently due to the ease of updating microcode. They do not use analog components; digital logic is standard. Although response time is excellent in hardwired units, microprogrammed units may have additional decoding steps. The use of basic combinational logic is more characteristic of hardwired units.

5. Fault Recovery

   In a situation where a microinstruction error is detected in a microprogrammed control unit, what is the usual advantage compared to a hardwired control unit?

   1. It requires manufacturing new integrated circuits to fix the issue.
   2. Both types require identical manual hardware adjustments to recover.
   3. It allows for correction by updating the microprogram instead of changing hardware.
   4. Errors can only be fixed by rewiring all logical paths.

   Explanation: Microprogrammed units can be repaired by modifying or reloading the incorrect microprogram, without needing hardware changes. Hardwired errors often require physical reworking, such as replacing chips or rewiring. Rewiring all logical paths and hardware adjustments are necessary for hardwired units but not microprogrammed ones. Manufacturing new integrated circuits is generally not needed to fix a microprogrammed unit.