Question

What is the amount of ROM needed to implement a 4-bit multiplier?

• A. 1 Kbits
• B. 2 Kbits
• C. 4 Kbits
• D. 64 bits

Hint:

ROM size for a combinational circuit = (Number of input combinations) $\times$ (Output bits).

Answer 1

The Correct Option is B

Step 1: Understanding inputs and outputs.
A 4-bit multiplier has two 4-bit inputs. Therefore, total input bits = $4 + 4 = 8$ bits.
Step 2: Calculating number of input combinations.
Number of possible input combinations = $2^8 = 256$.
Step 3: Determining output size.
Multiplying two 4-bit numbers produces an 8-bit result.
Step 4: Calculating ROM size.
Each of the 256 input combinations stores an 8-bit output.
Total ROM size = $256 \times 8 = 2048$ bits = $2$ Kbits.
Step 5: Final conclusion.
Therefore, the amount of ROM needed to implement a 4-bit multiplier is 2 Kbits.