What is the difference between packed bcd and unpacked bcd?

Answer 1

BCD:
A byte (unpacked) representation of a decimal digit in the range0 through
9. Unpacked decimal numbers are stored as unsigned byte quantities. One
digit is stored in each byte. The magnitude of the number is determined from
the low-order half-byte; hexadecimal values 0-9 are valid and are
interpreted as decimal numbers. The high-order half-byte must be zero for
multiplication and division; it may contain any value for addition and
subtraction.

Packed BCD:
A byte (packed) representation of two decimal digits, each in the range
0 through 9. One digit is stored in each half-byte. The digit in the
high-order half-byte is the most significant. Values 0-9 are valid in each
half-byte. The range of a packed decimal byte is 0-99.