RE: LIC

-----Original Message-----
From: Larry Bolhuis [mailto:lbolhui@ibm.net]

David,

> Actually the way that OS/400 does this is to keep a translatable "source" of
the
> program with the executable, with enough smarts to know when to throw away the
> old executable and build a new one.

  True. But it also never lets the programmer 'see' the hardware so there is
always a way to create the new executable.

> This could be done on virtually any
> platform, as long as that platform always included a program that could read
and
> translate this "source".  Granted, this would be more difficult on a platform
> that didn't have a stable equivalent of the TIMI, but it's certainly not
> impossible.

  While it could be done, It would mean new compilers at the point where they
started supporting it.  A big part of the issue is that the applications are
written expecting certain limits exist for register sizes, page sizes, address
spaces etc because programmers are allowed to access them!  Simply translating
these type apps to a platform with bigger registers, pages, more address space
etc, does nothing for the app but let it run.  Wintel gets most of that by
emulation in the hardware.  To do it right requires the compilers not have
pre-set limits in them or make them so large that they are basically ignored.
Also they must eliminate hardware access by the programmer.  Then have the
compiler generate code that emulates the huge registers, memory sizes etc on the
hardware of the day.  Of course this causes overhead in the generated code when
you don't need those huge registers or address spaces.   Sound a lot like
SLIC???  It is a big task which involves more than just compiler changes.

 - Larrry

------------------------------

Larrry <grin>,

Yeah, it's definitely not a trivial task, particularly for languages like C.  It
just seems odd to me that a concept that has worked so well on the S/38 and
AS/400 for 20 years hasn't been more widely embraced, at least for languages
that limit programmer access to the hardware anyway (like, say, COBOL).  The
Java byte-code stuff is the closest thing out there, and that's still new enough
to be shaky.

Dave Shaw
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