13 Mar
2005
13 Mar
'05
4:58 p.m.
On Sun, 13 Mar 2005 20:36:58 +0100, Eric Smith <eric at brouhaha.com> wrote:
Ethan writes about bytes on the PDP-10:
...
A byte is the smallest INDIVIDUALLY addressable unit of data on a system.
It was usual to speak of a character when a part of a whole word was
extracted. I do not remember any details of the Univac 1107 (I only
programmed in FORTRAN and Simula on it), but I think the normal character
was six bits. I am fairly certain that was not a byte, it was extracted
from an 18-bit halfword or a 36-bit word. A byte is something you can load
and store to an individual address, and the hardware takes care of the
rest. A character needs some software or firmware mapping in order to read
or write just one of them.
--
Bj?rn
On the -10,
one stores 6 6-bit characters in a machine word, and one speaks of
bytes that are 6 bits.
Not necessarily. On the PDP-10, the byte size could be anywhere from
zero (really!) to 36 bits. Seven bits was the most commonly used for
general ASCII text, with one leftover bit per word. In fact, this
was so common that the KS10 CPU has special dedicated hardware to make
the 7-bit byte case more efficient than the other supported byte sizes.