GATE | Gate IT 2005 | Question 49

n instruction set of a processor has 125 signals which can be divided into 5 groups of mutually exclusive signals as follows:
Group 1 : 20 signals, Group 2 : 70 signals, Group 3 : 2 signals, Group 4 : 10 signals, Group 5 : 23 signals.
How many bits of the control words can be saved by using vertical microprogramming over horizontal microprogramming?

(A) 0
(B) 103
(C) 22
(D) 55


Answer: (B)

Explanation:
In horizontal microprogramming, each control signal is represented by one bit in the microinstruction.
Therefore, total number of bits of the control words required in Horizontal microprogramming :
= 20 + 70 + 2 + 10 + 23 = 125 bits

In vertical microprogramming, ‘n’ control signals encoded into log2 n bits.
group 1 : log2 20 = 5 bits
group 2 : log2 70 = 7 bits
group 3 : log2 2 = 1 bits
group 4 : log2 10 = 4 bits
group 5 : log2 23 = 5 bits

Total number of bits required in vertical microprogramming = 5 + 7 + 1 + 4 + 5 = 22 bits

So, number of bits saved= 125 – 22 = 103 bits.

 
Thus, option (B) is correct.

 
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