Why does a decimal value waste memory space?

Answer 1

Decimal (more formally, binary coded decimal) values store numeric information as digits encoded using the four bit binary equivalents: 0 (0000) to 9 (1001). That means a single byte can hold values between 0 and 99. But simply using the same byte to hold a binary value will yield values between 0 and 255 (or –128 and +127).