BCD vs. pure binary — “A Binary-Coded Decimal (BCD) representation of a given numeric value always requires more bits than its pure binary representation.” Evaluate.

Difficulty: Easy

Correct Answer: Correct

Explanation:


Introduction / Context:
Binary-Coded Decimal encodes each decimal digit with a fixed 4-bit nibble (0000–1001 valid). Pure binary uses the minimum number of bits needed to represent the numeric value by powers of two. This question contrasts representation efficiency for the same value across these two encodings.

Given Data / Assumptions:

  • BCD: 4 bits per decimal digit; 10–15 patterns are unused in standard BCD.
  • Binary: minimum-length base-2 positional representation.
  • We compare equal numeric values, not different numbers.


Concept / Approach:
Because BCD allocates four bits per decimal digit regardless of magnitude, it is wasteful compared to binary. For example, the decimal value 99 needs two BCD nibbles (8 bits) but only 7 bits in pure binary (1100011). This overhead persists and grows with larger magnitudes, so BCD invariably uses at least as many—and typically more—bits.

Step-by-Step Solution:

Pick a value (e.g., 45). BCD uses 0100 0101 (8 bits).Pure binary(45) = 101101 (6 bits).Compare lengths: BCD > binary → statement holds.


Verification / Alternative check:

Generalize: For an n-digit decimal number, BCD uses 4n bits. Binary needs ceil(log2(value+1)) bits, which is always ≤ 4n.


Why Other Options Are Wrong:

Incorrect: Contradicts length analysis.True only for numbers above 99: Counterexample with 45 shows it already holds.Depends only on endianness: Endianness changes byte order, not bit count.


Common Pitfalls:

Assuming “4 bits per digit” equals efficiency; many patterns are unused.Confusing BCD with packed decimal formats that still use 4 bits per digit.


Final Answer:

Correct

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