ASCII was actually invented in the US in the 1960s, as a 
  standardised way of encoding text on a computer. ASCII 
  defined 128 characters, that's a character for half of the 
  256 possible bytes in an 8-bit computer system.

Uh? Wouldn't it be easier to just say that it's a 7-bit coding system? And what does he mean by "256 possible bytes in an 8-bit computer system"?