Mainframe

A very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously.

Mainframes (often colloquially referred to as "big iron"^[1]) are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.

The term originally referred to the large cabinets that housed the central processing unit and main memory of early computers.^[2][3] Later the term was used to distinguish high-end commercial machines from less powerful units.

What is a mainframe Part I