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
Binary integer decimal encoding, it is encoded as a series of "p" decimal digits (using the densely packed decimal (DPD) encoding). This makes conversion to decimal form efficient, but requires a specialized decimal ALU to process. In the binary integer decimal (BID) encoding, it is encoded as a binary number. Using the fact that 2 = 1024 is only slightly more than 10 = 1000, 3"n"-digit decimal numbers can be efficiently packed into 10"n" binary bits. However, the IEEE formats have significands of 3"n"+1 digits, which would generally require 10"n"+4 binary bits to represent. This would not be efficient, because only 10 of