AS/400 9404 and TWINAX questions...

From: Ron Hudson <>
Date: Wed Sep 29 09:24:31 2004

On Sep 29, 2004, at 3:51 AM, Don Hills wrote:

> Ron Hudson <> wrote:
>> In one of my jobs I worked for the communications product div of
>> Novell,
>> they were trying to port netware to the AS400, but the simulated
>> machine the
>> AS400 presents was not effiecient for Novell, they could not get the
>> server
>> to run well enough, And IBM would not release the actual machine
>> instruction
>> set so the server could be written at the lower level (AS400 machines
>> all
>> run a simulator of an imaginary machine.. They do this so that all
>> models of
>> the AS400 are binary-compatible.)
> The actual machine instruction set was available for the System/38
> (AS/400
> predecessor). It was sufficiently baroque that no-one wrote anything
> for it
> so they didn't bother publishing it for the AS/400 where, as you say,
> they
> wanted to use different processor architectures within the range.
> That's not
> to say it was badly designed, it was simply highly optimised for its
> role as
> an OO database engine. There's a very interesting book about the
> AS/400's
> design process written by the chief architect, Frank Solti: "Inside the
> AS/400" ISBN 1-882419-66-9

My impression was that the different models of AS400 could have
different processors (and
native instruction sets) so to have upward/downward compatibility IBM
had them all run
an emulator of a machine that spoke "MI". They didn't want people
writing for the native
processor because the program would be bound to a single model.

(I suppose there would also be some security issues, if you can get
your own program running
at the same level as MI)

>> I think the imaginary machine's instruction set was called "MI" for
>> Machine
>> Interface???
> Yep.
> --
> Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
> It's ironic that people who are too smart to engage in politics
> are governed by people who are not as smart.
Received on Wed Sep 29 2004 - 09:24:31 BST

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