[HECnet] 2.11BSD

[Johnny Billquist]

On 2012-12-18 19:05, Clem Cole wrote:
Paul.   given the time (late 1960's/early 70's) the prevailing page sizes were 64   / 128 / 256 / 512 bytes which just happen to map to the sizes of blocks used in disk controllers.   1/4/8 k pages were a few years in the future.

by the virtual address extension to the 11 ( aka 1975 's vax 11/780) DEC switched to 512 bytes.

That said as wnj would point out in the "fast vax" paper by 1979 512 bytes was to small.

Um... The page size of the PDP-11 is 8K. :-)

	Johnny


Clem
On Dec 18, 2012, at 9:45 AM, <Paul_Koning at Dell.com> wrote:


On Dec 17, 2012, at 6:01 PM, Johnny Billquist wrote:

On 2012-12-17 23:50, Boyanich, Alastair wrote:
...
2) Was 2.11BSD ever ported to other platforms? Given the age/era, I'm
curious about 8088/8086/NECv20/80286 given the banked memory models used
and looking at the 8088/8086 XENIX disassembly.

Nope. That would not have been 2BSD then. And since the PDP-11 don't even have banked memory, it would probably cause some headaches to port 2BSD to something like 80286 or other similar machines.
To make it clear - the PDP-11 have a very normal MMU with pages.

Semi-normal.   It's rather unusual in that it has a paged MMU with page address granularity different from the page size (64 bytes vs. 8k bytes).   Most architectures have those two match, that avoids an adder -- consider VAX or MIPS or Alpha.

      paul




-- 
Johnny Billquist                                   || "I'm on a bus
                                                                  ||   on a psychedelic trip
email: bqt at softjar.se                         ||   Reading murder books
pdp is alive!                                         ||   tryin' to stay hip" - B. Idol