ASCII is a 7-bit code, which provides for 128 possible letters, numbers, or characters. To understand why this is, you need to know a little bit more about how binary works. For each bit, a code can either have a value of 1 or 0. So a 1-bit code can only have 2 possible outcomes: 1 or 0. A 2-bit code can have 4 outcomes: the first spot can be a 1 or 0, as can the second spot. 2×2=4. Each additional bit doubles your number of possible combinations. So 7-bits provides 2x2x2x2x2x2x2 possible combinations…or 128.