Paul wrote:
Maybe a good test is to look at program addresses. If
those look like
byte addresses -- though often they will have alignment rules -- then
I'd call the beast byte addressable. By that test, Alpha and PDP-11
clearly are, and PDP-10 and CDC 6000 clearly are not. (That assumes
von Neumann machines -- it doesn't help with Harvard machines.)
The IBM 7030 Data Processing System (aka STRETCH) used 64-bit words,
but used bit addressing for all integer and logical operations, and an
instructions operated on one or more "digits" of from 1 to 8 bits, up to
a total of 64 bits. However, it was generally considered by its developers
to have an 8-bit "byte" due to using an 8-bit character encoding, and in
fact that is the origin of the word "byte".
Instructions were 32 or 64 bits, and the branch instructions addressed
a half-word. Floating point instructions addressed a full word.
The address field was in the same position in all instructions, but for
the instructions that addressed words or half words the rightmost bit
positions were "stolen" for other uses.
Eric