[HECnet] 2.11BSD

[Clem Cole]

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. 

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