Is there any shortcut to find no of decoders needed to build a RAM of particular size?


#1

4.A RAM chip has a capacity of 1024 words of 8 bits each (1K × 8). The number of 2 × 4 decoders with enable line needed to construct a 16K × 16 RAM from 1K × 8 RAM is
a.4
b.5
c.6
d.7


#2

Answer: (B)

Explanation:

RAM chip size = 1k ×8[1024 words of 8 bits each]
RAM to construct =16k ×16
Number of chips required = (16k x 16)/ ( 1k x 8)
= (16k x 2)
[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

Hence 4 + 1 = 5 decoders are required.