
CPU of the Day: IBM Micro/370 – True Mainframe on a chip (2013) - pmarin
http://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro-370/
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StillBored
"Today’s System z, itself an evolution of the original System/360 and 370, can
still run many of the original programs, unmodified, from 50 years ago. This
is a testament to 2 things, the wide adoption of the IBM systems, and the
forward thinking of IBM."

Or rather the crazy levels backwards compatibility and effort to build what is
basically a hardware emulator for a 50 year old machine. Put another way, IBM
isn't making native ficon disks, they build a fancy controller that uses
SAS/etc disks and presents them as ficon, which runs on the same physical
transport as fiber channel, rather replacing much of the protocol stack. The
resulting MOD3 or MOD9/etc disks appear like 3390 model 9 disks circa the late
80's early 90's. AKA instead of a room sized disk they are basically virtual
with all the overhead that implies.

The CPU's are of course native, but like all the other ISA's reflect a more
modern design style of basically cracking the CISC instructions into an out of
order superscalar CPU and only using "micro code" for the really complex
instructions.

~~~
Shivetya
while the iSeries (think AS/400) has a shorter history many programs compiled
to earlier versions run on later versions due to the separation of hardware
layer from operating system layer. The system can recompile existing programs
without human usable/retrievable source due to the method use to encode them.

there is code from the eighties running in slightly updated form on our z and
even the i series systems have twenty year old code. both systems have web
facing extensions that directly map to older code (as in, green screen
3270/5250 that has no change to its code) pretty much seamlessly. new code is
often employed as necessary but the idea that stuff that worked well that is a
decade or more old still works today is what amazes me about the various IBM
platforms

~~~
bluedino
So much of our iSeries code has _(c) 1979_ in the header. Nearly 40 years.

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protomyth
That would have been pretty useful during my college years. Most of the
classes were on a IBM 370. I still have my assembly book and the assembly
banana book. XEDIT was an interesting editor.

It was an interesting era since pretty much everyone trudged over to the
computer lab to use the terminals to do their assignments. It does generate a
bit of community in groups of people going through their degree at the same
time.

It would have been interesting if IBM had got Motorola to second source the
chip and used it instead of the 8088. Would have been a very different PC era.

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ChuckMcM
Nick gave an excellent talk about this chip at the 1995 Microprocessor Forum
(which was around the 25th anniversary of the IBM/370). It was really
impressive that IBM could make the PC using the 8086 architecture because
there was such corporate alignment around the 3x0 architecture for all
computing that was IBM. Nick mentioned that in some ways the PC division felt
threatened by the notion that he had created a way to have the 370
architecture go "from top to bottom" on their product line.

~~~
watertom
The PC was created due to the consent decree. IBM was __forced __to use other
people 's processors, OS, hardware interfaces, etc. If it wasn't for the
consent decree the world would look very different.

~~~
B1FF_PSUVM
We were getting personal computers one way or another, there was a growing
tide of CP/M machines inching forward by 1980.

The IBM label on the product of a skunkworks division in Florida just put the
blessing of Mercury on that particular outcome.

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kev009
The /370 vision of a single chip mainframe was realized, I think the article
ends prematurely. The first card I've actually seen as such is the P/370 and
that may have been a productized version of this chip. There were some other
skunk works projects that might predate that
[http://www.garlic.com/~lynn/2002d.html#4](http://www.garlic.com/~lynn/2002d.html#4).

As others pointed out "real" S/390s also switched to CMOS microprocessors in
the 90s. There's some good reading in
[http://ps-2.kev009.com/ohlandl/P390/s390_i-
o_continues.txt](http://ps-2.kev009.com/ohlandl/P390/s390_i-o_continues.txt)
on the evolution of the I/O subsystems because I/O is what makes mainframes
interesting :)

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YZF
I had the joy of using the XT/370\. It was extremely cool to see the
"mainframe" run in a box. But it was dog slow compared to a single user
session on the mainframe (which IIRC was a 4341).

The 360/370 is/was an incredible architecture. It supported virtualization
decades before anyone outside a small group of people even knew what that was.
The instruction set was rich and easy to use which was important as a lot of
stuff got written in it directly those days. Unlike Unix which was mostly
written in C most of the 370 OSes of the time were written in assembly.

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nickpsecurity
That's neat as heck. A mainframe on a M68K for under four grand? I'd have
believed the emulation but not the price if someone told me. The RISC
workstations were so expensive. Add the word mainframe to a lower price than
that & I'd assume you were selling me a lemon. Haha.

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PaulHoule
Note that the IBM 9672 was the first actual mainframe with a CMOS
microprocessor circa the early 1990s. Now all mainframes are powered by
microprocessors.

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bogomipz
From the article:

"Not all processors are designed this way, some designs,known as random logic,
the op codes control the actual hardware directly"

An interesting note is that the name "random logic" comes from the fact that
when you look at a photomicrograph of a hard-wired CPU design you don't see
any discernible geometric patterns like you do on a microcoded CPU.

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twoodfin
The end of the (excellent) article mentions IBM's next minicomputers were
80386-based. Which were these?

~~~
skissane
I presume it is really talking about PS/2 systems running OS/2 or AIX, even
though they weren't commonly called "minicomputers".

~~~
B1FF_PSUVM
Right, minicomputers were the fridge-sized Vaxen and their ilk.

(Speaking of fridges, that was the era of 'computer rooms' with raised floors
and positive pressure air conditioning at a fairly small scale - might have
one serving one or two dozen people. Comms were poor.)

