Depends the processor. For the 11/45 class processors, you had a 17th address bit, which was the I/D choice. For the 11/40 class you shared the instructions and data space. So you had to use overlays and thunks at lot sooner.

On Tue, Jan 6, 2015 at 2:57 PM, Milo Velimirović <milov@cs.uwlax.edu> wrote:

Bringing a conversation back online.
On Jan 6, 2015, at 6:22 AM, arnold@skeeve.com wrote:

>> Peter Jeremy scripsit:
>>> But you pay for the size of $TERMCAP in every process you run.
>
> John Cowan <cowan@mercury.ccil.org> wrote:
>> A single termcap line doesn't cost that much, less than a KB in most cases.
>
> In 1981 terms, this has more weight. On a non-split I/D PDP-11 you only
> have 32KB to start with. (The discussion a few weeks ago about cutting
> yacc down to size comes to mind…)

(Or even earlier than ’81.) How did pdp11 UNIXes handle per process memory? It’s suggested above that there was a 50-50 split of the 64KB address space between instructions and data. My own recollection is that you got any combination of instruction and data space that was <64KB. This would also be subject to limits of pdp11 memory management unit.

Anyone have a definitive answer or pointer to appropriate man page or source code?

Thanks,
Milo

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