What is excess notation? What is twos complement notation? Why are they needed? In other words, why can't integer values be represented by ordinary binary numbers?

See the explanation below.

Explanation:

Excess notation is refers to a form that is used as a representation of signed integers or numeric values. In excess notation, the sign is assigned the first bit of the representation, and all positive numbers are represented by 1 while negative numbers are resented by zeros.

Twos complement notation is a technique of signed number representation in which positive numbers are encoded as ordinary binary numbers and negative values encoded as the complement of the directly related positive value with the addition of 1.

Therefore, integer values be represented by ordinary binary numbers because a technique of notation denotes choices that are specific in relation to ease of manipulation, numeric range, and accuracy.