And, once again, historical accident and American industrial predominance are at the heart of the matter. The keys on a computer keyboard are really just buttons that, when pressed, send electrical signals to the computer. Change the mapping and the same keycode will map to an entirely different character code. This is really a very clever scheme, providing a great deal of flexibility. By simply changing the keyboard mapping table you can get a different keyboard layout without having to build a brand-new keyboard.
Computers use binary arithmetic.
Hence, dividing computer memory into chunks divisible by the number two makes engineers' and programmers' lives easier. With seven bits, you can have 128 possible combinations. Add just one bit, and you double the number of combinations to 256. Needless to say, all these code pages were identical for the first 128 characters and varied widely among the next 128, although most IBM code pages retained at least some of the line-drawing characters in the same character positions between code pages. If you wanted to write, for example, in Icelandic, your computer would need a keyboard mapping table to create an Icelandic keyboard layout, an Icelandic code page, and a new chip for your computer's display adapter that contained the Icelandic glyphs.