Multiple choice

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

  1. 4

  2. 5

  3. 6

  4. 7
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B Correct answer
Explanation

RAM chip size = 1k × 8 [1024 words of 8 bits each] RAM to construct =16k × 16 Number of chips required = $\dfrac{16k +16}{1k + 8}=16 \times 2$ [16 chips vertically with each having 2 chips horizontally] So, to select one chip out of 16 vertical chips, we need 4 × 16 decoder. Available decoder is – 2 × 4 decoder. To be constructed is 4 × 16 decoder.

So, we need five 2 × 4 decoders in total to construct a 4 × 16 decoder.

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