"I have been running a full IBM System/370 Mainframe on a $5 Raspberry Pi Zero for ~5 years."

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Marvellous! He mentions the turnkey system emulator in question, by Jürgen Winkelmann:
The MVS 3.8j Tur(n)key System (Tur(n)key Level 4-)

**********************************************************************
*                                                                    *
* MVS 3.8j Tur(n)key 4- ("TK4-") is a ready to use OS/VS2 MVS 3.8j   *
* system built specifically to run under the Hercules System/370,    *
* ESA/390, and z/Architecture Emulator. It is an extension of the    *
* original MVS Tur(n)key Version 3 System ("TK3") created by Volker  *
* Bandke in 2002. See the User’s Manual for credits and copyrights.  *
*                                                                    *
* Note: TK4- does not claim to be a new release of the original TK3  *
*       system, hence its name is TK4-, not TK4.                     *
*                                                                    *
**********************************************************************

Where do you get a PI for $ 5?
That I find that hard to believe. A IBM 370 was the same as good 386 PC.Not having windows makes a machine
fast.

I don’t think the $5 is the important bit. A pi zero is nominally £5 here in the UK, but of course there’s postage and other overheads. It’s really not the important point.

What this thread introduces is the existence of a very capable emulator which can run on very cheap hardware.

What it introduces is simply how powerful modern hardware is and, honestly, how little power commercial back room data processing really consumes.

Back then we had more effcient (for the computers) data formats. We used data structures designed to be as efficient as practical on really bad hardware.

All of those efficiencies add up to make legacy software “extra” fast on modern hardware.

But in the end, it’s still legacy software. Software today is hard enough to use as it is, back then it was even more difficult because much of the constraints of the hardware leaked out to the end user experience. But as a rule, we simply put up with it back then.

Now, of course, we only have as anecdotal evidence that the software actually runs properly with no real data on it’s overall performance. How long does compiling all of the source code take on the Pi compared the mainframe it came from. On a legacy mainframe, it wouldn’t surprise me if the Pi was notably faster. But on a modern mainframe, I’m sure the Pi lags behind. But that doesn’t mean its unusable.

But, having replaced many a “mini” mainframe (no bigger than 3 or 4 washing machines lined up in a row) with machines that were either pizza box sized or mini-towers, it’s always nice to see them reduced to something the size of an index card.

And I thought the RAID USB drives was a nice touch.

Now you can put a 360 in your old washing machine
and emulate a IBM 360 with a Hard Drive. Card Punch/Reader optional at extra $$$. I/O is what ,made the old machines interesting. Does the PI emulate 360/370 microde? A important point for 360/370 emulation.

In the US, MicroCenter retail stores. The Pi Zero W is $5.