[Info-vax] OT: obscure PDP11 OSes (even more dinosaury)

[Dirk Munk]

bill at server3.cs.uofs.edu (Bill Gunshannon) wrote:
> In article <mlouja$7aj$2 at dont-email.me>,
> 	Simon Clubley <clubley at remove_me.eisner.decus.org-Earth.UFP> writes:
>> On 2015-06-15, Dirk Munk <munk at home.nl> wrote:
>>>
>>> The PDP-11 was a 16 bit architecture. Writing larger programs on a
>>> PDP-11 always involved using overlay. I've spend many hours trying to
>>> construct my Cobol programs in such a way that I could use memory
>>> resident overlay. Otherwise it would become disk-resident overlay, and
>>> that involved lots of extra disk IO as the name suggests. That would
>>> make an application a lot slower. Using RMS in supervisor mode also was
>>> a must to keep a somewhat fast application.
>>>
>>
>> The TKB overlay functionality (and it's associated documentation) is
>> something I have _very_ gladly left in the past and have almost
>> successfully purged from my memory. :-)
>>
>
> Having spent the least of my PDP-11 time on RSX I can't say how hard
> it was to use TKB but I do overlays on Ultrix-11 and have never found
> it particularly difficult.
>
> bill
>
No, it isn't difficult, unless you try to do memory resident overlay. It 
has to do with certain memory boundaries, the part of the program that 
remains in memory can't be to big, and the overlays can't be to big 
either. If I remember correctly the boundaries were magnitudes of 4kB.