What is this?

Z/OS is a mainframe operating system.

Also one of the few OSes that was already "WebAssembly" everywhere back in 2000.

It is called language environments.

https://www.ibm.com/docs/en/zos/2.4.0?topic=zos-language-env...

IBM i and Unisys ClearPath MCP (nee Burroughs) are two other examples still being comercialized.

What do you mean “was WebAssembly?”

All the ideas that many folks sell as being invented by WebAssembly were already present in such systems.

"Target audience: New and experienced students and professionals looking to build a technical understanding of the IBM Z mainframe."

I don't think that would be a very large audience, but I wonder how people actually do learn about ZSeries. I know there is an official Developer Thing Z/pDT or some such, that I gather is a mainframe emulator.

This is a reasonable introduction.

https://www.ibm.com/z/resources/zxplore

There's also a bunch of (sign-in required) free training at learn.ibm.com. And I think there's something on Coursera too.

It's definitely not a very large audience, and it is mostly people who either have to maintain a legacy system or want to integrate with one. The price/compute ratio on Z Series is terrible, but it is still highly effective for some workloads. Really though, anyone doing development on a Z Series today is almost certainly just maintaining a legacy core system.

Excuse my ignorance but where is this used these days?

Many of the core systems that run industries like financial servies, healthcare, and travel were built using COBOL and run on IBM Z Series mainframes. Almost nothing new is built on these platforms, but a lot of really mission critical systems still use it.

The Changelog Podcast had a good talk with someone who teaches mainframes and helps people get jobs.

"This week we’re talking about mainframes with Cameron Seay, Adjunct Professor at East Carolina University and a member of the Governing Board of the Open Mainframe Project. If you’ve been curious about mainframes, this show will be a great guide." https://changelog.com/news/mainframes-are-still-a-big-thing-...

I'm 31 years old, and I know TSO, CICS, 3270, TSO, ISPF, JCL, etc. I've coded in COBOL for a year for banks.

I've also emulated z/OS using the Hercules emulator, and managed to get it to boot (it's really wierd, unlike every other virtualized system I've played with, this one actually needs two 3270 clients to start it), and I've managed to write some COBOL, but I gave up when my JCL wouldn't compile the code, I was used to easy ways to compile and version control using proprietary software like Serena Changeman, so starting from scratch was too tedious for my purpose (of just having fun with computer stuff).

Did your employer(s) spring for your training, and did you have access to a mainframe?

There wasn't anything particularly difficult to learn for the purpose of just maintaining and adding simple code that is required to keep up with banking regulations in France, so yes my employer gave me some documents and left me to train alone for 1-2 weeks, learned everything I mentioned, and also the coding process and specificities required by the client (code standards, like GOTOs were of course forbidden, you had to give proper names to variables, reuse existing SQL statements and extend them if needed), as well as how to document the tests and deploy to staging, production etc.

And technically the access we had to the mainframe was the 3270 sessions we used to code, launched on a modern PC connected to a secure VPN connection to the mainframe. Using F7-F8 to scroll code was awful, and having only a single screen to switch back and forth when debugging CICS was awful but doable.

I wish we could have had access to modern ways of coding COBOL with real IDEs with syntax highlighting done locally, and then transmitted to the MF when you save. Never tried that, and I guess I'll never need to anymore.

Looks like a decent set of videos.

Security breaches are a regular news item these days. Haven't heard of any on a mainframe.

It would be neat if they just started making it easy to use it on an experimental basis. There's virtually no hobbyist community despite the availability of Hercules and a largely compatible but old system to run on it. Without mindshare it will be very hard to find people who can figure this stuff out, and it will die out.