> - yes, your software will continue to run, because that's what the mainframe is for

Maybe if you are using zos without any niche configuration. IBM has discontinued many mainframe platforms in the past, and there's no guarantee that next year they won't approach you with a 10x markup on your renting costs, that will become 50x in a couple of years and will keep going up until you decide to stop paying.

> yes, it will scale with whatever transaction volume you need in the future, because that's what the mainframe is for

Only if you gave-up on data dependency from the beginning. Transactions here means independent data processing, with possible rollbacks, not the relational concept people got used to on databases. If one needs relational data, it won't scale. NoSQL can scale with non-relational data too, it's not an exclusivity of mainframes.

> yes, you can get 99.999999999999999% uptime, because you have reliability built into the platform in astounding depth

That one is ridiculous. Uptime is limited by business code bugs, network and power outages, integration problems, and well, all that causes 90% of the downtime on a single-server shop. All the mainframe promises is that the hardware won't be a problem.

> yes, we'll happily help develop new functionality and support your in house staff in managing this system; the mainframe can actually detect faults and arrange a service call.

Yes, mainframes come with support contracts. You can get support for other platforms too, with the advantage that you won't need to hire IBM.

Anyway, none of that changes the fact that nobody wants to start using a mainframe nowadays, and that the people using them are either looking on how to replace them or avoiding increasing their usage. IBM will certainly be able to milk that market over the medium term, even more if they keep increasing their prices. They revenue may even go up for a while. But that's not thriving.

You are completely missing the point. I'm not arguing that any other solution can't offer the same kinds of things that the mainframe can.

Imagine you are a CIO. You have mainframe apps. Everything I said is true of your existing solution. If you keep it as is, it works just fine for the foreseeable future. Every other way forward requires a total rewrite of systems that have been stable for years and are typically mission critical financial and transaction processing systems.

That's what I mean by IBM having a compelling offering.

Problem is you can't keep it long term. As CIO you are also aware that the code has some ugly parts that are hard to maintain. You are also well aware of the cost to update the code (tax laws, or new features). You are very well aware of how hard it is to hire anyone competent who is willing to work in the language that it uses - mainframe languages are seen as a dead end. There is a lot less risk long term in leaving the mainframe behind, the only question is can you there without destroying the company.

There are advantages to the mainframe, but there are disadvantages too. As a CIO your job is to consider both.

I wonder if one of the bigger arguments is that there's no way you can really migrate in a way that doesn't actually cost you more money in the short term.

Even if you say "March 14, 2021 is the grand final feature freeze for the Mainframe, and day one of the Cloud Initiative", it's not going to happen. You're not going to have a MVP for several years, and a full replacement for five million undocumented lines of COBOL for even longer. Production fires will have to be fought. Regulators will demand you change something, and won't be keen to hear "we're supporting it in the Cloud Initiative, which customers will see in 2025." So you're gonna be writing quite a few more cheques to IBM and your team of COBOL jockeys.

After 5 or 6 years, as you've unloaded most of the customers to your painstakingly built replacement, you can finally begin to scale down the mainframe staff and perhaps return/downgrade some of the rented hardware.

Given that, it may be less a put-your-own-head-in-the-guillotine move just to spend those years hiring in a few new graduates with the promise of "We'll apprentice you to handle our unique and obscure codebase, and as long as you show up 40 hours a week and don't take a dump on your manager's desk, you're going to have a reliable paycheque for the next 20 years."

Do mainframes only run on COBOL? What are these languages? Or is it that some program written in 1972 is still running everything at United Airlines today?

My understanding is at least Java is well supported on mainframes. It's not the latest greatest language, but it sure beats ALGOL.

They run most anything from common to rare. The problem isn't the language, it is the years of cruft that never was fully documented. The people who made the early design decision are probably dead. Same problem any code you write today will have it is still in use in 50 years. Well maybe not quite as bad, if you paid attention you know some modern best practices that didn't exist then.

I had some colleagues who had worked on mainframe operating systems tailored for the airlines (PARS), and it's built upon TPF as I understand it. I don't know which language(s) it's implemented in, but I do recall them talking about assembler having a major role.

Java, C, C++ and Fortran, POSIX environments as well.

Then Algol, COBOL, RPG, NEWP, PL/I.

> IBM has discontinued many mainframe platforms in the past, and there's no guarantee that next year they won't approach you with a 10x markup on your renting costs, that will become 50x in a couple of years and will keep going up until you decide to stop paying.

Which ones has it discontinued? I thought once the 360 platform got going, it was basically forever (unbroken chain of compatibility). What am I missing?