Addressing the "why" part of the question - from my point of view as an assembly-code programmer on PDP-11 and VAX, the "standard" radix is most usefully chosen to match the instruction layout.
PDP-11 had 8 registers and 8 operand-mode indicators. Its double-operand instruction layout was
1 bit generally byte/word indicator (b)
3 bits opcode (o)
3 bits ...
The when and why of use of hexadecimal over octal representation
is intimately tied in with where and what: the use of one over the
other depended greatly on environmental factors, as well as the
machine itself, with programmer preference mainly being developed by
the influence of these.
As Raffzahan points out, IBM 360 environments used hexadecimal
When and why
That is quite close tied to the IBM /360 and its introduction in 1964. The /360 is based on the use of an 8 bit byte, 32 bit word (16 bit half word) and 24 bit address. Thus all basic memory items were multiples of 8 bit units - which are, without any remainder, best be displayed in hex. In addition displaying bytes in hex correlates well with ...
Minicomputers and mainframes typically used octal, as many early mainframes had word sizes that were a multiple of 3 bits, and so did some minis. Operators and engineers within those environments became used to this, so even power-of-two word size minicomputers kept using octal.
Microcomputers, however, almost always had power-of-two word sizes for both ...
Since the 'Manchester Baby' is mentioned above, I thought I might mention this one, since it's very interesting, for those who may accept game-sprite like objects instead of text, although I don't.
The MIDSAC computer computer had a billiards game in 1954, very impressive .
This all was driven by cost. The vertical and horizontal synchronization signals as well as the separate RGB signals had to be combined on the graphics card if using composite video. This greatly complicated the card and ran up the cost. It also complicated the graphics display as the display had to use circuitry to separate out the component parts of the ...