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From: gah4 <gah4@u.washington.edu>
Newsgroups: comp.compilers
Subject: Re: ancient PL/I, was fledgling assembler programmer
Date: Sat, 25 Mar 2023 01:27:18 -0700 (PDT)
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On Saturday, March 25, 2023 at 12:09:30 AM UTC-7, gah4 wrote:

(snip)

> 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.

Traditional overlays are generated by the linkage editor, and have
static offsets determined at link time.

PL/I (F) uses OS/360 LINK, LOAD, and DELETE macros to dynamically
load and unload modules.  The addresses are not static. IBM says:

    "The compiler consists of a number of phases
     under the supervision of compiler control
     routines. The compiler communicates with
     the control program of the operating
     system, for input/output and other
     services, through the control routines."

All described in:

http://bitsavers.trailing-edge.com/pdf/ibm/360/pli/GY28-6800-5_PL1_F_Program_Logic_Manual_197112.pdf

They do seem to be called phases, but there are both physical and
logical phases, where physical phases are what are more commonly
called phases. There are way more than 100 modules, but I stopped
counting.

(snip)
> [Never heard of dynamic overlays on S/360. -John]

It seems not to actually have a name.