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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

 

Note:it is previous yr gate ques , i asked it again bcz that answer i did not get. After getting answer i hide it. So don't close it.
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RAM chip size is 1K × 8  =213

To construct 16K × 16 RAM =218

total output lines 218/213 =25

 number of 2 × 4 decoders with enable line  hence

25/23=22

hence 4 decoder required

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No we need 5 decoders as number of address lines are 16K/1K = 16, so we need to realise 4X16 decoder to 2X4 decoder. We can do the same by 16/4 = 4 decoders and for these 4 decoders we also need one more decoder. So total 5 decoders are needed.
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Capacity of RAM Chip = 1k*8 bit

MEMORY CAPACITY = NUMBER OF CHIP * ONE RAM CHIP CAPACITY

Number of chip = memory capacity / one chip capacity

# chip =16k * 16bit / 1k * 8bit

# chip =(16 * 2 ) = 32 chip       ➔➔➔  (16 * 2 ): Meaning is there are 16 Rows , where 2 chips in each rows . 

so,we could required (4 * 16) Decoder , Now get ( 4* 16) Decoder using ( 2* 4) it would be like below…

so the number of decoder of size(2*4) is 5