Mainframes
Mainframes are large computer systems. They are extremely reliable and built to handle large workloads. Most mainframe owners are large corporations and government organisations. At the moment, there are probably 1,000 mainframe owning organisations worldwide (my estimate). Their number has decimated during the past 15 years, because of the high software license costs and because of mergers and acquisitions among mainframe owning companies. In 2000, when I was still selling mainframes for IBM, the estimated number of mainframe owners was estimated at 10,000.

I will add more mainframe info to this website in the future.