Presumably they don't run forever and are eventually upgraded... Well, let's assume they do run forever since we're talking mainframes, even then there would be

Presumably they don't run forever and are eventually upgraded... Well, let's assume they do run forever since we're talking mainframes, even then there would be the occasional upgrade. What happens to the old ones? Presumably it's not like standard servers and workstations where you end up finding 100 pages of Old Dell servers on eBay, but they have to go somewhere, no? Straight to the shredder?