Legacy Systems Maintenance

What's wrong with "legacy" systems which just WORKS and makes VALUE for people?

When you've got a system that is, for example, underpinning your whole business operation (eg billing, machine controls, whatever) and that cost thousands (often tens or hundreds of thousands) to implement and it only works on a legacy version of an operating system (be that Win 3.11, Linux 2.4, or even just XP) you WILL move heaven and earth to avoid disrupting that system.Even if it's a smooth migration to a current release, it doesn't have 15 years of perfect history behind

There are production systems that run on 30+ years old software. Upgrade for a sake of upgrade is often a wrong decision.

AFAIK it's because their entire system is rather legacy, so over the years they tacked on fixes while "the replacement will be done soon(TM)".Banks do have some problem with these sorts of projects, so I think they're trying to build something that will last as long as the COBOL system at less cost.

It's not 10 years, it's probably closer to 100. Reasons being a) the ridiculously large cost of rewriting and testing the new system on a real-time system that can't be taken down, and b) the ridiculously low cost of maintaining the current systems.

I've seen that with a core banking system. A decade later it's still running, with many patches in other systems to avoid its shortcomings. there's still no viable plan for migration.Just because you don't invest in a system doesn't mean it becomes obsolete.

It's all about pretty short term returns of course.You can build a web interface separately (external contract ofc) and that will work in parallell, but aside from very basic services there are tons of edge cases, bad documentation, business customers with systems built with yours as a dependency. It's a little like any bank old enough still having paper file storage and the planned end of life is the literal death of all paper holding customers.So the old system sticks around an

Tell me again how it’s cheaper to keep crappy legacy systems running rather than upgrading?

Usually, there is some legacy system behind the scenes that can't be updated because reasons. Not an excuse, but it isn't always that easy.

And it's not obscure systems powering typewriters in a dimly lit basement! We're talking banks, grocery stores, warehouses. Anything that was made 40+ years ago and was never re-engineered either because they couldn't or wouldn't. The price to upgrade is higher than the price to maintain so why bother? Not everyone cares about the latest trends.Edit: I said 20+ years initially.. but that's 2003 now :( So 20+ years from 20 years ago.