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

The 80186, 8086, 8088 and "Real Mode" on 80286 and later processors used a 20-bit segmented memory addressing system. The 80286 had 24 native address lines and then the 386 and later had either 32 or 64.