I read some years ago - IIRC the letters pages of BYTE, which dates it - about a critical factory control system in a company somewhere running on an IBM XT. The MFM drive had started to show some errors, so they got in touch with IBM, who being IBM, did not have any drives in stock (they'd stopped making them 15 years previously), but could retool a manufacturing line and make some. They offered to do it for $250k/drive. The company paid up.
That was cheaper at that time, than modernising that system. But it's clearly not long-term scalable.
I've heard of S/360s in KTLO mode in basements keeping banks running. Teams of people slowly crafting COBOL to get new features in at a cost of thousand of dollars a day each, and it "still works". But from a risk point of view, this is also ridiculous.
Safety critical systems have different economics. Yes, you can keep the floppy systems going, but the cost of keeping them going is rising exponentially each year, and at some point a failure will cost one or more airliners full of civilians and the blame will be put on not having a reasonable upgrade policy.
Sometimes you have to fix things before they stop working, or the cost is not just eyewateringly expensive in terms of dollars, but of human lives too.
IBM mainframes can run software written in the 1960s without modification. There’s no reason anyone would keep using an obsolete mainframe, and IBM usually leased them anyway and would refuse to support obsoleted machines.
You clearly don’t know what has been happening in the World of S/360 (and similar), support contracts in recent years.
Costs are rising heavily. IBM sold off most of that business, to people who don’t really want it as the skill base to support it is retiring and it’s too expensive to easily replace. This has been going on for a couple of decades, but it’s now gaining more and more pace.
That was cheaper at that time, than modernising that system. But it's clearly not long-term scalable.
I've heard of S/360s in KTLO mode in basements keeping banks running. Teams of people slowly crafting COBOL to get new features in at a cost of thousand of dollars a day each, and it "still works". But from a risk point of view, this is also ridiculous.
Safety critical systems have different economics. Yes, you can keep the floppy systems going, but the cost of keeping them going is rising exponentially each year, and at some point a failure will cost one or more airliners full of civilians and the blame will be put on not having a reasonable upgrade policy.
Sometimes you have to fix things before they stop working, or the cost is not just eyewateringly expensive in terms of dollars, but of human lives too.