mainframes

/M EY1 N F R EY0 M Z/
noun
  1. 1

    A large, powerful computer able to manage very many simultaneous tasks and communicate with very many connected terminals; used by large, complex organizations (such as banks and supermarkets) where continuously sustained operation is vital

Source: https://en.wiktionary.org/wiki/mainframe, https://en.wiktionary.org/wiki/mainframes