Decimal computer 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 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
Decimal floating point example, a significand of is encoded as binary , with the leading 4 bits encoding 7; the first significand which requires a 24th bit (and thus the second encoding form) is 2 = . In the above cases, the value represented is: Decimal64 and Decimal128 operate analogously, but with larger exponent continuation and significand fields. For Decimal128, the second encoding form is actually never used; the largest valid significand of 10−1 = 1ED09BEAD87C0378D8E63FFFFFFFF can be represented in 113 bits. In this version, the significand is stored as a series of decimal digits. The leading digit is between 0 and 9