Bi-quinary coded decimal

Bi-quinary coded decimal is a numeral encoding scheme used in many abacuses and in some early computers, including the Colossus. The term bi-quinary indicates that the code comprises both a two-state (bi) and a five-state (quinary) component.

Several different representations of bi-quinary coded decimal have been used by different machines. The two-state component is encoded as one or two bits, and the five-state component is encoded using three or five bits. Some examples are:

IBM 650 – 7 bits (two ‘bi’ bits: 0 5 and five ‘quinary’ bits: 0 1 2 3 4) with error checking (exactly one ‘bi’ bit and one ‘quinary’ bit set in a valid digit); in the picture of the front panel below, the bi-quinary encoding of the internal workings of the machine are evident in the arrangement of the lights (active bits are just visible)

Value	05–01234 Bits	IBM 650 front panel
0	10–10000
1	10–01000
2	10–00100
3	10–00010
4	10–00001
5	01–10000
6	01–01000
7	01–00100
8	01–00010
9	01–00001

UNIVAC Solid State – 4 bits (one ‘bi’ bit: 5 and three binary coded ‘quinary’ bits: 4 2 1) with 1 parity check bit

Value	p-5–421 bits
0	1–0–000
1	0–0–001
2	0–0–010
3	1–0–011
4	0–0–100
5	0–1–000
6	1–1–001
7	1–1–010
8	0–1–011
9	1–1–100

Univac LARC – 4 bits (one ‘bi’ bit: 5 and three ring counter coded ‘quinary’ bits) with 1 parity check bit

Value	p-5-qqq bits
0	1–0–000
1	0–0–001
2	1–0–011
3	0–0–111
4	1–0–110
5	0–1–000
6	1–1–001
7	0–1–011
8	1–1–111
9	0–1–110

Bi-quinary coded decimal

See also