Why is number of bits always(?) a power of two?

Question

We have 8-bit, 16-bit, 32-bit and 64-bit hardware architectures and operating systems. But not, say, 42-bit or 69-bit ones.

Why? Is it something fundamental that makes 2

Answer 1

Because the space reserved for the address is always a fixed number of bits. Once you have defined the fixed address (or pointer) size then you want to make the best of it, so you have to use all its values until the highest number it can store. The highest number you can get from a multiple of a bit (0 either 1) is always a power of two