Answer 3—The “weight” of a data code is a measure of how many of the bits in the code are ones. For example, an 8-bit code that has 256 values has weight values running from 0 to 8.

A limited-weight code uses extra bits to reduce the range of weights required to represent the same set of values. For example, you could add a ninth bit to an 8-bit code, creating an extremely simple limited-weight code by following the following rules: If the weight of the 8-bit code is 0–3, set the ninth bit to one. If the weight of the 8-bit code is 4–8, invert the 8-bit code and set the ninth bit to zero.

You can see that the 9-bit code has a weight of 1 to 4 in the first case, and a weight of 0 to 4 in the second. The overall range of weights for the 9-bit code is half that of the original 8-bit code.

Contributor: David Tweed