I think I read on HN recently that McDonald's restaurants' accounting ran on PDPs (10?) until the 90s. Can't find any info online to back that up though.
Wouldn't surprise me. Code that works has a tendency to stick around longer than people think. There's a lot of institutional knowledge built into that codebase. It would be like firing an employee of 20 years who works for nothing and hiring someone for millions of dollars.
Inertia is vast for the core systems that power large organizations. But these legacy systems do eventually yield as new requirements render change non-negotiable. Those ancient, messy, arcane, yet somehow supremely reliable systems tend to become frozen reflections of the organization they serve. It does eventually make sense to replace them when the organization has changed sufficiently that the reflection is no longer accurate.
New regulations, new products, new markets, new acquisitions, divestment, outsourcing... these are the real drivers of change that move an organization’s technology forward - not the new tech itself.
Because maintenance and replacement (in some way) is good practice. Quit thinking of tech as some magic thing that will never go bad and start thinking of it like any other piece of equipment. Regular maintenance is required. Replacement may be required.
Fun fact: SCO Unix started out as Microsoft Xenix, which started out as a license of Unix:
"Microsoft, which expected that Unix would be its operating system of the future when personal computers became powerful enough, purchased a license for Version 7 Unix from AT&T in 1978"
