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Comment by anonfordays | Hacker News Reader

>Who uses mainframes nowadays and what for?

Do you have a credit card? Do you bank in the USA? If you answered "yes" to either of the above questions, you interact indirectly with a mainframe.

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By that, do you mean banks, payment networks or both? And I guess I'd be curious as to why mainframes versus the rest. It seems like the answer for "why" is mainly because it started on mainframes and the cost of switching is really high, but I wonder if there isn't more to it.

Edit: Oh yeah, just saw MasterCard has some job posting for IBM Mainframe/COBOL positions. Fascinating.

Both. Mainframes though are incredibly good for both I/O and uptime.

Yeah, Linux/Unix are way better on both than they used to be, but on a mainframe, it's just a totally different level.

Not just that. Most operating systems lie about when an IO transaction completes for performance reasons. So if you lose power or the IO device dies you still think it succeeded. A mainframe doesn't do that... it also multiplexes the IO so it happens more than once so if one adapter fails it keeps going. The resiliency is the main use case in many situations. That said IME 99.995% of use cases don't need a mainframe. They just don't need to be that reliable if they can fail gracefully.

You can run Linux on mainframes fine. RHEL has first-class support for s390x / Z.

Yes! I had the good fortune of working with z/VM for Linux guests. It was a lot of fun and it worked quite well.

Core transactions and ledgers run on these. Bank I work for now (contracting job) uses them as their core system.

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