[TUHS] 2.11 BSD question... (exe sizes)

John Cowan cowan at mercury.ccil.org
Wed Aug 11 13:49:34 AEST 2010

Jason Stevens scripsit:

> I'll admit I'm not all that swift on the pdp-11, but I get the impression
> that the maximum exe size is 128kb with 64kb of instructions, and 64kb of
> data?  Isn't there something that can be done with overlays or some other
> linker thing to act like an 8086/80286 with the large memory model (ie
> multiple segments...?)

The PDP-11 is inherently a 16-bit-pointer machine; it has no concept
of 32-bit pointers, so it is always either in the x86 small or the x86
tiny model.  On DEC's operating systems, you could indeed set up overlays
that allowed code to be swapped in and out, either to disk or to unmapped
physical memory (much quicker!)  However, AFAIK ld(1) never provided that
capability to userspace, although the technique is used inside the kernel.
In any case, such tricks don't help with data space, which is strictly
limited to 64K.

There is / One art                      John Cowan <cowan at ccil.org>
No more / No less                       http://www.ccil.org/~cowan
To do / All things
With art- / Lessness    

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