Mainframe (big iron)

A mainframe (also known as "big iron") is a high-performance computer used for large-scale computing purposes that require greater availability and security than a smaller-scale machine can offer. Historically, mainframes have been associated with centralized rather than distributed computing, although that distinction is blurring as smaller computers become more powerful and mainframes become more multi-purpose. Today, IBM emphasizes that their mainframes can be used to serve distributed users and smaller servers in a computing network.