<data> (BCD, packed decimal) A number representation where a
number is expressed as a sequence of decimal digits and then
each decimal digit is encoded as a four-bit binary number (a
nibble). E.g. decimal 92 would be encoded as the eight-bit
sequence 1001 0010.

In some cases, the right-most nibble contains the sign
(positive or negative).

It is easier to convert decimal numbers to and from BCD than
binary and, though BCD is often converted to binary for
arithmetic processing, it is possible to build hardware that
operates directly on BCD.