So now you know: Code converters are used for more than protecting private information from spies. In 4-bit binary, subtracting binary is equivalent to adding and vice versa.
Suffice it to say that the Excess-3 BCD system has some properties that made it useful in early computers. When you speak into the cellular phone, an encoder converts the sound of your voice into electrical signals — which can travel very fast over very long distances.
Because a 4-bit integer can only hold values 0 to 15, an excess of 6 means that any sum over 9 will overflow produce a carry out.
Excess-3 arithmetic uses different algorithms than normal non-biased BCD or binary positional system numbers. Portability and tractability are not technical terms.
Motivation[ edit ] The primary advantage of excess-3 coding over non-biased coding is that a decimal number can be nines' complemented  for subtraction as easily as a binary number can be ones' complemented : just by inverting all bits.
It is also more difficult to write the zero pattern to magnetic media. For instance, after adding 1 in excess-3 and 2 in excess-3the sum looks like 6 in excess-3 instead of 3 in excess