Question: "what is mainframes"? how do u explain it to anyone?
Answer: The simplest way of identifying a mainframe is by the operating system that it runs since almost all mainframes run one of the following operating systems.
Also when disussing mainframes you don't refer to THE hard drive since they usually have at least several dozen if not hundreds. Some mainframes measure their hard drive storage in the number of acres of land that the drives occupy. Sizes will certainly be in petabytes or greater rather than the miniscule gigabytes and terabytes of smaller systems.
Also you don't have one computer screen attached to a mainframe computer, you have a few hundred or tens of thousands of PCs attached to use as monitors instead.
This article written by Stephen Chapman, Felgall Pty Ltd.