Question

In the design of a control unit of a processor, two common approaches are used: hardware control and microprogrammed control. Consider the following statements: 

I. Hardware control units are generally faster but more difficult to modify than microprogrammed control units. 
II. In a horizontal microprogrammed control unit, each control signal has a separate bit in the control word. 
III. Vertical microprogramming leads to longer control words but provides greater parallelism. 
IV. Microprogrammed control units are typically easier to implement and modify than hardware control units.

• A. I, II, and IV only
• B. I, II, III, and IV
• C. II, III, and IV only
• D. I, III, and IV only

Hint:

In microprogramming, horizontal control units provide greater parallelism, while vertical microprogramming reduces control word length but with limited parallelism.

Answer 1

The Correct Option is A

Step 1: Let's analyze the statements: 

- I. Hardware control units are faster, but their design is more rigid and difficult to modify compared to microprogrammed control units, which are flexible and easier to modify. Thus, this statement is true.
- II. In horizontal microprogramming, each control signal is represented by a separate bit, making it more parallel but also increasing the control word length. This statement is true.
- III. Vertical microprogramming typically has shorter control words but sacrifices parallelism because fewer control signals are available. This statement is incorrect, as vertical microprogramming usually does not provide greater parallelism.
- IV. Microprogrammed control units are generally easier to modify and implement compared to hardware control units, which are hardwired and less flexible. This statement is true.

Step 2: Based on this analysis, the correct answer is (a) because statements I, II, and IV are correct, while statement III is incorrect.