Binary coded decimals (BCD) numbers express each digit as a ___________

Binary Coded Decimal (BCD) is a method of representing decimal numbers in binary form by encoding each individual decimal digit (0-9) separately, rather than converting the whole number to a single binary value.

Since a decimal digit can range from 0 to 9, at least four binary bits are needed to represent it, because \(2^4 = 16\) possible combinations are enough to cover all ten digit values (0000 to 1001 are used, while 1010 to 1111 are unused). A group of exactly four bits is called a nibble, which is half of a standard 8-bit byte.

So in BCD, every decimal digit of a number is stored as its own 4-bit nibble. For example, the decimal number 47 would be stored as 0100 (representing 4) followed by 0111 (representing 7), two nibbles placed side by side rather than one combined binary value.

A common confusion is mixing this up with a byte, which is 8 bits and normally holds two BCD digits (one nibble each), or with a single bit, which can only represent two states (0 or 1) and cannot encode a full decimal digit on its own.

Exam tip: whenever a question links "4 bits" with "one decimal digit," the term being tested is nibble, not byte or bit.