When my wife was working for Honeywell, in the 1980s, one of the customers she had dealings with was British Telecom.
BT, at one location, had what they called the “orange LEOs”.
Now, for those who don’t know this, the LEO was the world’s first-ever commercially-oriented machine (1951). Even more amazingly, the Lyons Electronic Office was designed and built by the J Lyons company, best-known as manufacturers of cakes and for their nationwide chain of corner tea shops.
Anyway, an “orange LEO” was an ICL 2900 mainframe (they came in orange cabinets), emulating an ICL 1900 mainframe, emulating a GEC System 4 mainframe emulating a LEO.
30+ year old executable code over 3 architecture changes…