---
title: "BCD code advantages and disadvantages"
subject: "Digital Logic"
chapter: 1
key: "semester_3/digital_logic:bcd-advantages-disadvantages"
source: https://www.bctengineer.com/q/semester_3/digital_logic/bcd-advantages-disadvantages
site: BCT Engineering
---

# BCD code advantages and disadvantages

Digital Logic · Chapter 1: Introduction

- Asked in: 2078 Bhadra, 1+3 marks
- Video: [Binary Coded Decimal (BCD) Code](https://www.youtube.com/watch?v=0rLiYpy2CqQ) — Neso Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/digital_logic/bcd-advantages-disadvantages
- Whole chapter: https://www.bctengineer.com/md/semester_3/digital_logic/chapter-1

## Question

What is BCD code? List the advantages and disadvantages of BCD code.

## Short answer

BCD codes each decimal digit 0–9 as 4‑bit 8421 binary. Advantages: easy decimal conversion, exact representation of decimal fractions, simple display interfacing. Disadvantages: uses more bits, six invalid codes, arithmetic needs correction (add 6) making circuits slower and more complex.

## Answer

**BCD (Binary Coded Decimal)** is a code in which each decimal digit 0–9 is represented by its own 4-bit binary value with weights 8-4-2-1. Codes 1010–1111 are invalid.
Example: $(57)_{10}$ = 0101 0111 (BCD).

#### Advantages
1. Very easy conversion between decimal and BCD, as each digit is coded separately.
2. Suitable for decimal displays (7-segment), calculators, digital clocks and meters, where numbers are shown to people.
3. Decimal fractions such as 0.1 are represented exactly, so it is used in financial calculations.
4. Easy to scale by powers of 10 (shift by one digit).

#### Disadvantages
1. Needs more bits than pure binary: $(99)_{10}$ needs 8 bits in BCD but only 7 in binary; storage is wasted.
2. Six of the 16 4-bit combinations are unused.
3. Arithmetic is more complex: after binary addition a correction (add 0110) is needed when a digit exceeds 9.
4. Circuits for BCD arithmetic are slower and more complex than binary circuits.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why is BCD suited to 7-segment displays and calculators?
   A. It uses fewer bits than binary
   B. It makes arithmetic simpler
   C. Each decimal digit is coded separately, so conversion to decimal is easy
   D. It has no unused codes
   Answer: C. Digit-by-digit coding makes decimal display easy. (Key point: Advantage)

2. Why is BCD used in financial calculations?
   A. It is faster than binary
   B. It needs fewer bits
   C. It detects errors
   D. Decimal fractions like 0.1 are represented exactly
   Answer: D. Pure binary cannot represent 0.1 exactly; BCD can. (Key point: Exact fractions)

3. What extra step makes BCD addition more complex?
   A. Add 0110 when a digit exceeds 9
   B. Subtract 0011 always
   C. Invert all bits
   D. Shift left by one
   Answer: A. Binary sums above 1001 need a +6 correction. (Key point: Arithmetic disadvantage)

4. How many bits does 99 need in BCD versus binary?
   A. 7 in BCD, 8 in binary
   B. 8 bits in BCD, 7 in binary
   C. 8 in both
   D. 4 in BCD, 7 in binary
   Answer: B. BCD wastes storage by coding each digit in 4 bits. (Key point: Storage)

## Related in Digital Logic

- [BCD code with examples](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Abcd-code-explain) — Digital Logic, chapter 1, asked 2×
- [BCD code and 3-bit binary-to-Gray converter](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Abcd-code-gray-converter) — Digital Logic, chapter 1
- [(1110)gray→BCD and (1430)₁₀→Excess-3](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Agray-to-bcd-decimal-to-excess3) — Digital Logic, chapter 1
- [Code conversions: (41.8125)₁₀, (1000)₂, (19)₁₀](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Acode-conversions-41-8125) — Digital Logic, chapter 1

## Related in other subjects

- [BCD counter 0-9999 on seven segment VHDL](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Avhdl-bcd-counter-seven-segment) — Embedded System, chapter 9
- [Importance of source coding; Shannon-Fano vs BCD (four symbols)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Asource-coding-sf-bcd-four) — Communication Systems, chapter 6