Large, expensive, ultra-fast computers. Used generally of number crunching supercomputers such as Cray?s, but can include more conventional big commercial IBMish mainframes. The term implies approval, in contrast to Dinosaur.%%%%%%
From: 
http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?query=bigiron
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This term has evolved a broader scope that also includes expensive x86 servers.
5 pages link to BigIron:
