Originally Posted by deepsand

All inputs fields have, regardless of any explicit definition, size limitations, owing to the physical limitations of the hardware. For example, the accumulator register in the CPU chip itself will physically allow no more that a fixed number of bits. Thus, when doing integer math, there is a numeric value above which it cannot accomodate.

It is not unusual, owing to the binary nature of the switches which form the circuitry of the hardware, for such limitations be some multiple of 2, particularly 2 raised to a certain power. In this case, 128 equals 2 to the 7th power.