I was told they did an assessment a year or two ago to price out what it would take to move the business completely off mainframe and onto an x86 stack. It was in the hundreds of millions of dollars to do so because so much other software has been built to interact with and rely on the mainframe over the years that switching off it would be a multi-year effort across every department in the company. So of course that ROI calculation was pretty damn easy and the mainframe isn't going anywhere.

So just... have the new server expose itself over the TN3270/TN5250 protocols, such that these interoperating systems see what they expect to see? (You could even build the new system as a regular REST API or something at its core, and then build the TN3270/TN5250 exposure as a separate gateway service on top, such that it'd be easy to shut it off later if everything finally moves off it one day.)

You don't necessarily need to move the $new project off the legacy hardware, just write it in such a way that you can do easily later.

I'm eliding many details here, but the principle stands.

- Spend $300,000,000 over 10 years moving to a new system, and hope that by the time you've done that it's not obsolete.

- Spend $1,000,000 a year on a system that still works.

You could run the system for 300 years for what it would cost to replace the system.

In spite of the collective wisdom on HN, there aren't a lot of companies in the world with hundreds of millions of dollars sitting around doing nothing. Even ones that work on mainframes.

- Spend $1.5 million maintaining the current system, but as bits get updated keep in mind the system that you'd like to have in 10 15 years time.

You're going to have to replace the system within 300 years anyway, you aren't saving that money, every feature you add that is reliant on the old system is literally technical debt, because eventually you'll have to rewrite it for the new system.

I'm not even saying you need to have a new system in mind, just keep in mind that you will be moving to a new system, so code appropriately.

And it will still be able to run all your programs that were written and tested since the late 20th century, by the kind of organic entity we used to call "human".

Slightly more serious retort: I'm not aware of any brands from 300 years ago, I'd be surprised if any of IBMs customers survive, let alone enough to keep IBM as a going concern.

Btw when you start folding the space time mesh, terahertz figures just become marketing numbers, what you really want to know is how many parsecs it can do the Kessel run in.

You might be, you just don't realize that they're hundreds of years old.

For example, the insurance company Lloyds of London is fairly well-known around the globe. It's 333 years old.

If anything, this is a sign that mainframe users have way too much profit for what should probably be commodity software.

Remember that these are large, public businesses. Explaining to shareholders that profits are going to take a noticeable hit for years because of IT investment that isn't strictly necessary is effectively a non-starter.

I wasn't thinking that. I was thinking more like when you add a new feature, fit it into an API that is portable. Or add a translation layer so the feature can be written how you would like system to be in the future, but it works on your hardware today.

2nd I'd say theres a half life of best practise. Over the 10 20 year tome frame, id expect some of what you were doing is going to become outdated yes, on the same way some of your knowledge over your career will become outdated, or the phone I your pocket will, you wouldn't use that as an argument against education, or buying that phone.

Btw, if its as costly to deal with the interface as with the mainframe directly, that's a win. The interface can move off the mainframe to somewhere cheaper/better.

It doesn't become wrong, it just evolves into another dead-end. The 3270 is an interface, too, but the reason everybody suggests replacing it or augmenting it is precisely because the spartan tooling and mindshare makes it expensive. As XML recedes into history it is likewise becoming more expensive as an interface.

I chose XML vs JSON because I figured it was a transition everybody was somewhat familiar with. And younger programmers have an almost visceral dislike of XML, which I thought might help get the point across--that an interface someone once thought (and probably still thinks) would help ease future interoperability becomes a reason or excuse for future programmers to avoid that integration.

> Btw, if its as costly to deal with the interface as with the mainframe directly, that's a win.

I think the problem is that you don't really know if it's as costly. The error bars on that sort of risk assessment are huge because our industry sucks at accurately predicting migration costs. And it sucks because complex software systems are intrinsically unique. Commercial solutions that claim to be able to capture and control all those dimensions of complexity tend to be sold by vendors with names like IBM and Oracle. Such vendors also pioneered interfaces like SQL, which is both a soaring achievement in terms of capturing complexity behind a beautiful interface while also falling epically short of what's needed to actually reduce long-term integration costs.

But alas, language has changed and these kids won't get off my lawn.

‘Whatever is fitted in any sort to excite the ideas of pain, and danger, that is to say, whatever is in any sort terrible, or is conversant about terrible objects, or operates in a manner analogous to terror, is a source of the sublime; that is, it is productive of the strongest emotion which the mind is capable of feeling.’