Why do bytes have 8 bits ?
They weren’t always like this. Older computers used to have “strange” (by today’s standards) word/byte sizes, usually multiples of 6. The 8-bit byte didn’t appear until the advent of IBM’s System/360. From the early 1970’s on, most computers used 8-bit bytes and multiple-of-8-bit words, and the non-standard became a de-facto standard. Now, why did the System/360 have 8-bit bytes ? Probably, because of the use of BCD data (or “packed decimal”); you need 4 bits to represent one digit (0-9), so one 8-bit byte can represent two digits. The System/360 had instructions that allowed one easily to handle BCD data, and that made much easier the lifes of people writing accounting systems. It would be hard to use 6-bit bytes to represent BCD, so 8 bits was the obvious solution. More information can be found in the Jargon File.
