Legacy stuff isn't the problem.
(This was first posted here: https://forums.theregister.co.uk/forum/containing/370244 roughly 8 years ago. Pardon the reference to the earlier thread in the third paragraph; I left it intact because it illustrates my point. The PDP11 code is still functioning as intended.)
Legacy stuff isn't the problem.
That's a myth.
There are running, functional systems, and there are broken systems. Legacy stuff that is still running, and functional is (by definition) not broken.
All of the examples listed in the 17 (at this moment) comments above are MANAGEMENT errors, and have nothing to do with the functionality of the systems being discussed.
The biggest management blunder is not having a plan for the future.
The second is not standardizing on functional systems (including upgrade path).
The third is not properly training staff in the use of those systems.
I have 30 year old machine code (running in a PDP11 emulator on Linux) that one client of mine is happy as hell to have ... It helps him keep track of a portion of his business that would otherwise require three or four pairs of technically trained eyes. (It's a specialty greenhouse, if you're curious ... the guy grows orchids, and keeps track of humidity, temperature, light levels, soil moisture, pH, salt, etc.). It originally ran on a pair of PDP11s (redundant systems ... hardware was flaky 30 years ago), now it's on a pair of dead-screen Pentium laptops that cost a total of $50. His electricity bill dropped, and the UPS powers the laptops for a little longer than the PDP11.
Is legacy stuff inherently "bad"? Nope. Bad management is, though.
(And then, about four days later: https://forums.theregister.co.uk/forum/containing/373033 )
Why are you trying to demonize "legacy"?
Old stuff isn't inherently bad. If it still performs the job it was intended to do, let it. If it doesn't, replace it. You DO have an upgrade path planned and budgeted for, right? No? Then I submit that it isn't an equipment problem, but rather it is a management problem.
I commented on my 30 year old greenhouse management software last time. This time, let's talk telephones. Palo Alto, that hot-bed of high-tech, still had analog switches in a couple of the local exchanges ... in 1998! They still worked for voice, and that was all the customers contracts paid for, so why change 'em? It wasn't until customers started getting upset that they couldn't connect to AOL at 28,800 "like my neighbor" that they switched to digital. The 326 exchange was the last to be changed over. If it wasn't for AOL, it would probably still be analog ... and some of THAT gear was installed in the late 1940s! (I was a NOC-monkey, lurking under Bryant Street and on Fabian(RIP) ... I'm probably going to have nightmares tonight over the memories ...)
Or consider TCP/IP. You use it every single day. Virtually everyone connecting to the Internet uses it for nearly every pointy-clicky intratubes delight. When was it first implemented? (See RFC 675 if you don't know the answer). It's a third of a century old, fer chrissake! Do you consider TCP/IP old, dusty, and in need of replacement? (Cue IPv6 fanbois ...).
Or how about the basic UNIX API?
Old stuff is NOT inherently bad, although there are bad installations. Bad installs are not the equipment's fault, rather they are the fault of the people controlling the purse strings.