Re: ancient PL/I, was fledgling assembler programmer

On Friday, March 24, 2023 at 9:13:05 PM UTC-7, Dennis Boone wrote:


(after I wrote)
> > OK, the IBM PL/I (F) compiler, for what many consider a bloated
> > language, is designed to run (maybe not well) in 64K.
> > At the end of every compilation it tells how much memory was
> > used, how much available, and how much to keep the symbol table
> > in memory.


> It's... 30-some passes, iirc?


> [Well, phases or overlays but yes, IBM was really good at slicing compilers
> into pieces they could overlay. -John]


It is what IBM calls, I believe, dynamic overlay. Each module specifically
requests others to be loaded into memory. If there is enough memory,
they can stay, otherwise they are removed.


And there are a few disk files to be used, when it is actually
a separate pass. The only one I actually know, is if the preprocessor
is used, it writes a disk file with the preprocessor output.


And as noted, if it is really short on memory, the symbol table
goes out to disk.


Fortran H, on the other hand, uses the overlay system generated
by the linkage editor. When running on virtual storage system, it is
usual to run the compiler through the linkage editor to remove
the overlay structure. (One of the few linkers that knows how
to read its own output.) Normally it is about 300K, without
overlay closer to 450K.
[Never heard of dynamic overlays on S/360. -John]

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