Bi-quinary

A bi-quinary code is one way of storing decimal digits using binary memory elements. 7 bits are used per digit: two bits are used to select between the 0-4 and 5-9 ranges, and 5 bits to indicate each of the 5 possible values in each range.

Although inefficient in storage terms, this representation allowed extensive error checking, since only 10 codes out of the 128 available were valid. Checking in hardware was simple, since only one bit was allowed to be on in each of the two fields.