Computer Data Representation

• This notation is another fixed length approach to representing negative and non-negative values.

• Contrary to excess notation this method employs a sign bit of 0 to represent the non-negative (+) sign and a 1 for the negative (-); again, zero is included in the non-negative set.

• One simple feature is that if the number is a non-negative, i.e., the sign-bit is a 0, it may be evaluated as in standard binary notation by simply sum up all the 1's then adding the "+" sign.

Encoding/Decoding a Non-negative (+) value:

• Note: For our purposes, the sign of non-negative values (including zero) is +.

• A 2's Complement number such as 0101 represents the signed value +5; the method for correctly interpreting the value requires that we ...

1. Take note of the sign bit 0 as the + sign.
2. Remember that when the sign bit is a 0, hence +, simply sum up the rest like a standard binary number and combine the sign and the sum.

The MSB is 0, of +; and the sum of the remaining bits, 101 = 5

Therefore the signed decimal value represented = +5

• However, evaluating a negative number involves a different conversion technique described next.