Mainframes

Mainframes (often colloquially referred to as big iron) are huge and expensive computers used mainly by government institutions and large companies for mission critical applications, usually bulk data processing such as censuses, industry/consumer statistics, ERP, and financial transaction processing.
The term originated during the early 1970s with the introduction of smaller, fewer complex computers such as the DEC PDP-8 and PDP-11 series, which became known as minicomputers or just minis. The industry/users then coined the term "mainframe" to describe bigger, earlier types (previously known simply as "computers").