Question

A RAM chip has a capacity of 1024 words of 8 bits each (1K x 8) . The number of 2 x 4 decoders with enable line needed to construct a 16K x 16 RAM from 1K x 8 RAM is 

(A) 4 

(B) 5 

(C) 6 

(D) 7

Answer 1

Correct option is (B) 5 

RAM chip size = 1k x 8 [1024 words of 8 bits each]

RAM to construct = 16k x 16

Number of chips required = 16k x 16 / 1k x 8 = 16x2 [16 chips vertically with each  having 2 chips horizontally]

So to select one chip out of 16 vertical chips, we need 4 x 16 decoder.

Available decoder is - 2 x 4 decoder

To be constructed is 4 x 16 decoder

So we need 5, 2 x 4 decoder in total to construct 4 x 16 decoder.