OS/2

From: Douglas Quebbeman <dhquebbeman_at_theestopinalgroup.com>
Date: Fri May 26 13:56:25 2000

> Don't forget that OS/2 was written by Gordon Letwin
> AT MICROSOFT!
>
>
> You might enjoy reading "Inside OS/2" by Gordon Letwin; from Microsoft
> Press.

While I agree OS/2 is a better operating system than Windows, this
book depressed me due to Gordon's wrongheaded-belief that a GPF
should always be considered an indicator of a programming problem.

Since Intel didn't give us a pointer fault, the GPF is the only
proper way to implement dynamic linking. As they shipped, OS/2
from version 1.0 to 1.2 never did properly implement dynamic linking;
and Windows inherits the wrong way from OS/2.

Strangely, Ed Iacobucci (who was Gordon Letwin's counterpart at IBM)
wrote an article that appeared in a magazine that described OS/2's
dynamic linking as operating the way it should.

The key difference is this: in real dynamic linking, CALL instructions
that are supposed to invoke procedures in a DLL are constructed in the
executable image such that when the processor executes the CALL, it
causes a GPF [pointer fault]; then the GPF handler looks at the faulting
instruction. If the pointer is a faulted pointer to a routine in a DLL,
then snap the link [map the DLL into memory and then modify the faulting
instruction to point to the entry point of the routine as described in
the DLL's export table], and restart the instruction. Otherwise, it's a bug
and you signal a condition which somehere generates an error message.
In this scenario, programs start up much faster because the OS is not
reading and linking every routine in the executable's import table. If
you never use feature <X> in the program, and if feature <X> resides
tottally in a separate DLL, then that DLL never gets mapped into RAM.
MUCH, MUCH better execution, more robust operation, in particular, the
machine wouldn't thrash at startup dur to all those programs in your
startup folder.

Due to Ed's article, I always assumed that there was a turf was between
IBM and Microsoft on this and other salient technical points. MS won
and was wrong.

So, having said that, you might see why I'm not a big fan of Letwin's.

Shew! Glad I got _that_ off my chest again.

respectfully submitted,
-doug quebbeman
Received on Fri May 26 2000 - 13:56:25 BST