Why in computers the bits length is always a power of two. 8 - 16 - 32 - 64 - 128 - 256... why not 5 6 7? what's the difference? could I please get an informative answer?

The basic group length is a byte. From the hardware design point of view it makes sense to use multiples of a byte when increasing size. Your statement isn't strictly true, however. 12-bit addresses were common in the early days of microprocessors. The Zilog Z8000 had a 24-bit address bus. Some floating-point representations also had oddball numbers of bits. As a matter of fact, a byte is not always 8 bits.

I know that such machines existed, but nobody considers them no more. Is there any mathematical or usage reason that the standard is 8bits multiplications. What I mean is, suppose it wasn't multiplies of 8, would there be something that cannot be calculated or done for mathematical, electrical or hardware reasons? thank u for answering

Ah yes. Why a byte isn't 8 bits? I learned in a PDP-11 course, in which they stated that Byte=8bits , but a Word is machine dependant. Correct me if I'm wrong... It's just that it drove me mad thinking about why it's usually a power of two.