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From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: more addressing, Why I've Dropped In
Date: Wed, 18 Jun 2025 18:19:55 -0000 (UTC)
Organization: Taughannock Networks
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Cleverness: some
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Originator: johnl@iecc.com (John Levine)

According to Stephen Fuld  <sfuld@alumni.cmu.edu.invalid>:
>>> On the System/360, a FORTRAN compiler typically compiled each subroutine
>> in a program separately from every other subroutine. They just got
>> linked together by the linking loader in order to run.
>
>I'm not sure what you mean by "linkingloader"  The linkage editor (IIRC 
>IEWL) linked together all of the object modules created by the compiler. 
>  Loading the program was a different operation, again IIRC, done by the 
>initiator in each partition)

OS and its descendants have both a linkage editor that combined a bunch of object
modules and wrote a load module on disk, and a loader that leaves the result in
memory and runs it directly.

The loader is not the same as program fetch, the part of the operating system
that reads and starts a load module.  Load modules (and object decks) notionally
start at location zero, and have a relocation directory that lists all of the
places there are address pointers that need to be adjusted to the actual location
where it's loaded.  That relocation was quite simple; the overlay loader did it
too and I believe was under 1000 bytes.

For people who want more details, I shamelessly recommend this book:

https://shop.elsevier.com/books/linkers-and-loaders/levine/978-0-08-051031-6

-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly