Question: Often I read about bigiron on mailing lists and the Internet forum. What is Big Iron and how it is related to UNIX system?
Answer: Big Iron is nothing but Mainframe computer for large data processing systems.
Big Iron is hacker term and refers to large, expensive, ultra-fast computers. It is used generally for number crunching supercomputers such as Crays, but can include more conventional big commercial IBM mainframes. It is widely believed that the term Big Iron was derived from early mainframes, which were enclosed in room-size metal frames.
Also, the term may be used to show respect to older large UNIX mainframe or supercomputers. Now, term is also used for modern supercomputers. Most commercial mainframe or supercomputers comes with UNIX or Linux.