The biquinary code is a higher- order code whose one component is binary and consists of two binary numbers, while the second is quinary and consists of five elements. It is a 2-out-of-5 code that was used in earlier computers and is also used to encode decimal digits. There is also a 2-out-of-7 code with two and seven elements.
In both codes, two bit positions are always occupied by "1", the remaining by "0". In the 2-out-of-5 code, the five bits are divided into two groups of 2 and 3 digits, with two bits serving checking purposes. Each bit of the group of five represents a particular decimal value, which from left to right is 7, 4, 2, 1 and 0. For example, the decimal digit 6 is formed by a "1" on the second and third bit positions, all other three bits are "0".
In the 2-out-of-7 code, the place value of the bit positions from left to right is 0, 5, 4, 3, 2, 1, and 0. For example, in this code, the decimal digit "0" is formed by a "1" on the first and last bit positions, all other five bit positions are "0"; a decimal "6" would be formed by a "1" on the third and fifth positions.