Arrange the following configuration for CPU in decreasing order of operating speeds:
Hard wired control, Vertical microprogramming, Horizontal microprogramming.
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Answer: B
The operating speed of a control unit depends on how control signals are generated and whether any decoding or memory access delays are involved:
- Hardwired Control: This design uses combinational and sequential logic circuits to generate control signals directly. Since there is no control memory access involved, it is the fastest configuration.
- Horizontal Microprogramming: In this microprogrammed approach, control signals are represented with little to no encoding (often one bit per control signal). While it requires a control memory access (making it slower than hardwired), it requires minimal decoding logic, making it faster than vertical microprogramming.
- Vertical Microprogramming: Here, control signals are highly encoded into fields to save control memory space. This requires an additional decoding step after fetching the microinstruction from memory, introducing extra propagation delay. Hence, it is the slowest of the three.
Thus, the decreasing order of operating speeds is:
Hardwired Control > Horizontal Microprogramming > Vertical Microprogramming
Therefore, the correct option is B.
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