28 Jun
2013
28 Jun
'13
9:21 a.m.
On 6/27/2013 11:37 AM, Rich Alderson wrote:
Remember, the PDP-10 is a word-addressed machine, not a byte-addressed
one.
I don't use a PDP-10 that often.
*Instructions* are 36 bits long (9 op code, 4 AC, 1
indirect, 4 index,
18 address/immediate). Bytes are defined by 36-bit pointers which
define the length of the byte, the position of the byte within the
word, and the address of the word containing the byte. Halfword
instructions refer to the left or right halfword of the word addressed.
Thank you for the reminder.
How do you fit that into an 18-bit machine based on an
8-bit byte?
(Hint: Look at DEC's 18-bit family to see what a real 18-bit system does.)
The point I was making was that 9 bit bytes are a better word size for
bytes. The PDP 11 went 8 bits and that we know in hindsight is just too
small.
Rich
Ben.