Binary-coded decimal: Difference between revisions

Revision as of 01:37, 25 April 2024

Revision as of 01:46, 25 April 2024

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While packed BCD does not make optimal use of storage (using about 20% more memory than [[binary notation]] to store the same numbers), conversion to [[ASCII]], EBCDIC, or the various encodings of [[Unicode]] is made trivial, as no arithmetic operations are required. The extra storage requirements are usually offset by the need for the accuracy and compatibility with calculator or hand calculation that fixed-point decimal arithmetic provides. Denser packings of [[BCD (character encoding)|BCD]] exist which avoid the storage penalty and also need no arithmetic operations for common conversions.

Packed BCD is supported in the [[COBOL]] programming language as the "COMPUTATIONAL-3" (an IBM extension adopted by many other compiler vendors) or "PACKED-DECIMAL" (part of the 1985 COBOL standard) data type. It is supported in [[PL/I]] as "FIXED DECIMAL". Beside the IBM System/360 and later compatible mainframes, packed BCD is implemented in the native instruction set of the original [[VAX]] processors from [[Digital Equipment Corporation]] and some models of the [[SDS Sigma series]] mainframes, and is the native format for the [[Burroughs Corporation]] Medium Systems]] line of mainframes (descended from the 1950s [[Burroughs 205|Electrodata 200 series]]).

[[Ten's complement]] representations for negative numbers offer an alternative approach to encoding the sign of packed (and other) BCD numbers. In this case, positive numbers always have a most significant digit between 0 and 4 (inclusive), while negative numbers are represented by the 10's complement of the corresponding positive number.