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

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

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.