Absolute fringe opinion(or is it?): The performance and reliability are awesome, but have nothing to do with the real reasons IBM mainframes are still around.

Absolute fringe opinion(or is it?): The performance and reliability are awesome, but have nothing to do with the real reasons IBM mainframes are still around. Backward compatibility helps - you can still run code for the IBM 1401 on these machines if you need to. When they came up with System 360, they effectively crystalized software development... taking what used to be a forced march to new hardware every few years as you got a new, faster, incompatible machine, and were rewriting the code for the better faster hardware.... and just FROZE that stream of development, which is why Y2K really happened. But even that's not the real reason IBM mainframes have stuck around so long... it's the same reason Virtualization and Containers took off.... they give no default access to files or disks, the administrator has to plan out which disks and other resources a Job, (or Runtime, VM, or container) will access. (Example, the DD statement of JCL[1]) This has the effect of being a very course grained capability object system.[2] The default access to everything on a Windows/Unix/Linux system just doesn't work in the modern era. It is because side effects can be strictly controlled, that Mainframes and later VMs and Containers have so much value. -- a small rant: It's 2023... consider the humble AC wall outlet, you can plug almost anything into it, and the circuit breaker or fuse will prevent bad things from happening to your wiring, house, etc. Why can't we protect against a rogue device plugged into a USB port? Why can't we just run any program we please, like we can plug in a lamp we bought at a garage sale, without risking everything? -- [1] https://www.ibm.com/docs/en/zos-basic-skills?topic=concepts-jcl-statements-what-does-dd-statement-do https://www.ibm.com/docs/en/zos-basic-skills?topic=concepts-... [2] https://en.wikipedia.org/wiki/Capability-based_security https://en.wikipedia.org/wiki/Capability-based_security