Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!tut.cis.ohio-state.edu!snorkelwacker!mit-eddie!uw-beaver!uw-june!kolding
From: kolding@cs.washington.edu (Eric Koldinger)
Newsgroups: comp.arch
Subject: Re: IBM RISC System/6000  AS/400 (actually a diversion on the topic)
Message-ID: <10947@june.cs.washington.edu>
Date: 4 Mar 90 12:03:49 GMT
References: <1990Feb28.042949.21952@edm.uucp> <1990Feb28.174838.7725@esegue.segue.boston.ma.us> <10901@june.cs.washington.edu> <2984@auspex.auspex.com>
Reply-To: kolding@june.cs.washington.edu (Eric Koldinger)
Distribution: usa
Organization: University of Washington, Computer Science, Seattle
Lines: 41

In article <2984@auspex.auspex.com> guy@auspex.auspex.com (Guy Harris) writes:
::   Yes, somewhat.  Some programs are translated to IMPI, the internal machine
::   language, which is interpreted by HMC, or what most people would call
::   microcode.  Others are left at the MI, or machine interface, which is the
::   same as the S/38 MI (and assembly language), I believe.
::
:::Different models of the AS/400 can and do have
:::different native microcodes.
::    
::    I think they all run the same micro-code.  At least they all run the same
::    VMC (vertical microcode).
:
:OK, so is VMC code that, in executable form, is in IMPI?

    Yes.  Much of it is essentially OS code, although it's part of the
    published architecture.  All VMC runs at the IMPI level.

:In that case, are you saying that the IMPI is the same on all the
:models?

    As far as I know, yes.  At least I think that this is the case currently.
    There is nothing that prevents the IMPI specification from being changed.
    Only the MI must remain stable.

:In that case, is there any reason (other than "it doesn't match what IBM
:calls them") not to call the HMC "the microcode", the VMC "machine
:language code", and the MI "some tokens in some interpretive language
:that sometimes gets compiled into machine code"?

    The problem with breaking it down this way is that IMPI can essentially
    be thought of as a moving target.  The MI is the published architecture,
    and all future AS/400's will conform to MI.  However, the IMPI can change
    quite radically.  All programs that are written at MI level will continue
    to run, even if they were translated from MI to IMPI (the os will take care
    of automatically retranslating them).

-- 
        _   /|                          Eric Koldinger
        \`o_O'                          University of Washington
          ( )     "Gag Ack Barf"        Department of Computer Science
           U                            kolding@cs.washington.edu