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
|
| 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
|
See also
