The first computer networks were built around a central computer called a "mainframe".
The mainframe is therfore a powerful central computer which controls user sessions at the various terminals that are connected to it. Thanks to this architecture it is possible to consolidate, i.e. centrally manage, all of a company's business applications.
However, in the mainframe model, system performance rests entirely on the performance capacity of the mainframe, for this reason it is sometimes referred to as "heavy computing". Also, in a mainframe environment, the network terminals can only see the mainframe server.