Arrange the following configurations for CPU in decreasing order of operating…

The speed of a control unit depends on how control signals are generated.

1. Hardwired Control

Control signals are generated directly using combinational logic circuits.

Example: RISC processors often use hardwired control for fast instruction execution.

• No microinstructions need to be fetched.

• Fastest control signal generation.

Therefore, Hardwired Control has the highest operating speed.

2. Horizontal Microprogramming

A microinstruction contains many control bits, each directly controlling hardware operations.

Example: A microinstruction may directly specify:

Load MAR = 1
Read Memory = 1
Increment PC = 1

Since control signals are generated directly from the microinstruction, little or no decoding is needed.

Therefore, Horizontal Microprogramming is faster than Vertical Microprogramming.

3. Vertical Microprogramming

Microinstructions are encoded and must be decoded before generating control signals.

Example: Instead of storing many control bits directly, an encoded field such as:

101

must first be decoded into the required control signals.

The extra decoding step increases execution time.

Therefore, Vertical Microprogramming is the slowest among the three.

Decreasing Order of Operating Speed
Hardwired Control > Horizontal Microprogramming > Vertical Microprogramming