bi-quinary coded decimal

Bi-quinary coded decimal is a numeral encoding scheme used in many abacuses and in some early computers, notably the Colossus. The term ''bi-quinary'' indicates that the code comprises both a two-state (''bi'') and a five-state (''quin''ary) component. The encoding resembles that used by many abacuses, with four beads indicating the five values either from 0 through 4 or from 5 through 9 and another bead indicating which of those ranges (which can alternatively be thought of as +5).

Several human languages, most notably Fula and Wolof also use biquinary systems. For example, the Fula word for 6, ''jowi e go'o'', literally means ''five lusone''. Roman numerals use a symbolic, rather than positional, bi-quinary base, even though Latin is completely decimal.

The Korean finger counting system Chisanbop uses a bi-quinary system, where each finger represents a one and a thumb represents a five, allowing one to count from 0 to 99 with two hands.

One advantage of one bi-quinary encoding scheme on digital computers is that it must have two bits set (one in the binary field and one in the quinary field), providing a built-in checksum to verify if the number is valid or not. (Stuck bits happened frequently with computers using mechanical relays.)

Examples

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 to five bits. Some examples are:
* Roman and Chinese abacuses
* Stibitz relay calculators at Bell Labs from Model II onwards
* FACOM 128 relay calculators at Fujitsu

IBM 650

The IBM 650 uses seven bits: two ''bi'' bits (0 and 5) and five ''quinary'' bits (0, 1, 2, 3, 4), with error checking.

Exactly one ''bi'' bit and one ''quinary'' bit is set in a valid digit. The bi-quinary encoding of the internal workings of the machine are evident in the arrangement of its lights – the ''bi'' bits form the top of a T for each digit, and the ''quinary'' bits form the vertical stem.

Remington Rand 409

The Remington Rand 409 has five bits: one ''quinary'' bit (tube) for each of 1, 3, 5, and 7 - only one of these would be on at the time. The fifth ''bi'' bit represented 9 if none of the others were on; otherwise it added 1 to the value represented by the other ''quinary'' bit. The machine was sold in the two models UNIVAC 60 and UNIVAC 120.

UNIVAC Solid State

The UNIVAC Solid State uses four bits: one ''bi'' bit (5), three binary coded ''quinary'' bits (4 2 1) and one parity check bit

UNIVAC LARC

The UNIVAC LARC has four bits: one ''bi'' bit (5), three Johnson counter-coded ''quinary'' bits and one parity check bit.

See also

* Binary-coded decimal
* Binary number
* Chisanbop
* Finger binary
* Quinary
* Two-out-of-five code
* FACOM 128

References

Further reading

* (NB. Supersedes MIL-HDBK-231(AS) (1970-07-01).)

{{DEFAULTSORT:Bi-Quinary Coded Decimal
Computer arithmetic
Numeral systems