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My Master's supervisor, at Wits university in Johannesburg, worked on the architecture of the 360 after graduating from the PhD program at Harvard. I remember him telling us how they went about deciding whether or not 32 bits would be a sufficient size for "most" floating point numbers. They were very systematic about it, scouring journals, talking with physicists and mathematicians and so on.

TIL that not only the software side was chaotic (served as the backdrop of Fred Brook's "Mythical Man Month"), but also the hardware side almost failed.

the article here ends around 1971 --- the mainframe would later save IBM again, twice, once when they replaced aluminum with copper in interconnects, and then when some crazy IBM Fellow had a team port Linux to s390. Which marked the birth of "enterprise Linux", i.e. Linux running the data centre, for real.

This whole thing is very cool and worth reading.

BUT. I worked at a place that used IBM 360s. We ran stuff for engineers, a lot of Fortran along with assembly code. We had so much stuff going on we could not code up and run things fast enough. The engineer/scientist got frustrated.

Then one day an engineer brought in an Apple II from home and ran the programs on that.

The earth shook. The very ground beneath us moved. Tectonic plates shifted. The world was never the same again! I think it was Visicalc.

Later there were other things. Soul Of A New Machine. The Mac.

I wonder how the compute power of a current high end smart phone compares with and IBM 360? I know the graphics chip is better.

Alan Kay has promulgated many famous truths about computer science - one of them being that among all fields of study, it has the least regard for the people and discoveries that brought it to where it is today. Maybe it's just my own sense of history as I move into my 4th and likely last decade of working with computers, but I find this to be both true and lamentable.

This was a great article - thanks for sharing!

The successor IBM Mainframes are still alive... for the time being.

https://www.redbooks.ibm.com/redbooks/pdfs/sg248329.pdf

The reason the tape drives are in those tall enclosures are the vertical channels below the tape reels. That was for slack in the tape, there was a loop of tape hanging in each of the channels, so that tape reads and writes could be stopped and started faster than the heavy tape reels could stop and start.

The IBM Centennial Film has a short interview with Fred Brooks about System/360: https://youtu.be/VQ0PBve6Alk?t=84

Set to some nice Philip Glass music to boot.

My sister worked at IBM and one of my favorite stories is when Lotus tried to pressure IBM to spend millions on licensing, a few engineers went off and built their own spreadsheet application and IBM told Lotus to piss off.

To add to this: they had $750 million in 1963 dollars, in parts and no shipping computers; inventory control was so bad that they had to have guys with clipboards to physically go into the warehouse and count parts.

They announced it and started getting a huge number of orders; IBM hired 1000 people a month and kept up that pace of hiring for 5 years.

I liked the Mad Men plot about the computer arriving in the office. Everybody was trying to decide how to react to it.

The well known book "The Mythical Man Month" is in large part based on the author's experience as one of the top people on the System 360 project, and what went wrong during the effort.

And this is all before integrated circuits, so the circuits are still very large, consisting of many circuits on boards mounted on a backplane.

https://en.wikipedia.org/wiki/IBM_System/360#Basic_hardware_...

https://en.wikipedia.org/wiki/Solid_Logic_Technology

Thomas Watson, Jr.'s A Business and Its Beliefs was published in 1963 and makes no allusion to the S/360 work. It makes for curious reading today, for unrelated reasons.

As an ex-IBMer, I miss the IBM of old. So much innovation. Now they are just a consulting company. So sad to see it go that way.

z boxes use a flavor of VM to run all the LPARS and allocate memory and devices. z/OS, z/VM and Linux all run as VMs.

Then there's CMS which runs under VM; theoretically it could run as an LPAR, but I've not seen that as running DIAGNOSE (VM system call) to the LPAR hypervisor could be disruptive. It would be interesting to drop DIAGNOSE into a z/OS environment, but I suspect it would be intercepted.

I much prefer z/VM to z/OS as a development environment. At one shop, I developed products under VM for deployment under both VM and MVS.

Many early S/360 installations ran 7070 and, I guess, 1401 emulators.

Eventually with VM, the SIE (Start Interpretive Execution) instruction appeared. A form is running LPARs.

i have also found these to be interesting, kind of selection/ analysis/ visualisation over memoirs of Lou Gerstner (part 2 is around s/360):

https://juliusgamanyi.com/2018/12/28/wardley-maps-an-illustr...

https://juliusgamanyi.com/2019/06/18/wardley-maps-an-illustr...

https://juliusgamanyi.com/2020/06/25/wardley-maps-illustrate...

Now, reading the article, this "[rivalry].. So intense was it that sometimes it seemed to exceed the rivalry with external competitors.” reminded me of something old about Motorola.. where rivalry went to the need to reverse-engineering other depts' chips via 3rd party acquiring them..

www.chicagomag.com/Chicago-Magazine/September-2014/What-Happened-to-Motorola/

This was some great read