Re:Linux dominates supercomputers as never before
by kjs3 on Friday June 27, 2014 @02:09AM
(#7952902)
The 11/45 has a 16-bit address space optionally expanded to 18-bits with an MMU so could do 256KB of memory. With the MMU, you could take advantage of split instruction and data memory, which gave a pair of 64k address spaces mapped into the 18-bit space.
No PDP-11 AFAIK have a separate, dedicated stack space. You're thinking of the 8k dedicated I/O page.
Re:Linux dominates supercomputers as never before
by hga on Friday June 27, 2014 @08:48AM
(#7953712)
Ah, yes, for the 11/45 I was referring to what a single program could do.
However, as I recall (from the very early '80s when I was using both a 11/44 and 11/45), the MMU had a 8 KiB page size, so the natural thing to do was to divide the data as described, so a stack overflow would trigger a trap. Although after a bit of time with Google, I note the 11/40 manual says all PDP-11s have a location in which to put a stack boundary, so maybe that was a convention which matched what the MMU could do.
Maybe not that much, it next moved to the first model of the PDP-11, which had a max of 56 KiB memory of 8 bit bytes. Then to an 11/45, which could do 64 KiB of code, 56 KiB of data and 8 KiB of stack.