RE: AS/4OO vs S/390 Linux port

["Richard Jackson" <richardjackson@xxxxxxxxxxxxxxxxxx>]

The address size is 31 bits because it was originally 32 bits but in the
60's somebody at IBM decided to use the high-order bit for something or
other and now IBM can't get it back unless they rewrite everybody's code
that relies on this goofy-ness.  In the 60s when main memory sizes were 32k
and 128k, no one could imagine a machine with 2 gigabytes of main storage.
In the 60's no one could imagine 2 gigabytes of disk either.  Because of the
31-bit XA addresses, the largest address value that can be directly computed
using the standard address registers is 2 gigabytes.  VM and MVS running on
S/390 will address much large address spaces but uses other hardware
registers and some black-magic programming to do it.

The S/390 doesn't have the most advanced hardware architecture.  It is
essentially an enhanced System/360 - nearly the same program status word
layout, the IO subsystem created for the S/370 and using a 370/168 as the
primary CPU was recently revised (last few years), 16 each 32 bit general
purpose registers, EBCDIC coding, microcoded hardware, CISC, but heavy
pipelining and other techniques to make it fast.  The 360/370/390 line was
early with very fast ECL logic that created so much heat that CPUs were
mounted in water-cooled Thermal Conduction Modules to keep them cool.  Lots
of pretty cool history there.

Whether the AS/400 Linux port is better will not depend on the hardware
platform.  If done correctly, it will depend on what _you_ think of it.  The
390 guys have years of practice making this antique hardware architecture
blow the doors off most other platforms.  They are very good at that.  There
has been a Unix port for S/390 for years.

Richard Jackson
mailto:richardjackson@richardjackson.net
www.richardjacksonltd.com
Voice: 1 (303) 808-8058
Fax:   1 (303) 663-4325

-----Original Message-----
From: owner-midrange-l@midrange.com
[mailto:owner-midrange-l@midrange.com]On Behalf Of David Bulog
Sent: Tuesday, August 15, 2000 2:23 PM
To: MIDRANGE-L@midrange.com
Subject: AS/4OO vs S/390 Linux port


With all the fuss aboubt the S/390 Linux port...........
I understand that the S/390 uses only a 31bit CPU.
Does that mean in effect that the AS/4OO architecture is more advanced
having a 64bit CPU & when the AS/400 Linux port is
ready it will be better?

Cheers Dave

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