Decimal computer

Decimal computers are computers which can represent numbers and addresses in decimal as well as providing instructions to operate on those numbers and addresses directly in decimal, without conversion to a pure binary representation. Some also had a variable wordlength, which enabled operations on numbers with a large number of digits.

Early computers

Early computers that were exclusively decimal include the ENIAC, IBM NORC, IBM 650, IBM 1620, IBM 7070. In these machines the basic unit of data was the decimal digit, encoded in one of several schemes, including binary-coded decimal or BCD, bi-quinary, excess-3, and two-out-of-five code. Except for the 1620, these machines used word addressing. When non-numeric characters were used in these machines, they were encoded as two decimal digits.

Other early computers were character oriented, but provided instructions for performing arithmetic on strings of character that consisted of decimal numerals. On these machines the basic data element was an alphanumeric character, typically encoded in 6 bits. UNIVAC I and UNIVAC II used word addressing, with 12 character words. IBM examples include IBM 702, IBM 705, IBM 7080, IBM 1401 and other members of the IBM 1400 series, including the IBM 7010. The IBM character machines nominally used decimal addressing, but some allowed the use of non-decimal characters in addresses to expand the available address space. Addresses referenced a single character encoded in 6 bits with two additional bits per character, a word mark and a parity bit. The word mark enabled operations on variable length words.