In the 1960s, however, this view was coming under a great deal of strain. Increasingly, telephone users wanted to conference call, forward, and record voice greetings, so common today. Such features required more flexibility in the controller, leading to the development of computer-controlled switching machines, notably the Bell Labs − Western Electric 1ESS. These early machines still had an analog, usually electromechanical switching matrix because the technology of the time did not permit the cost-effective dedication of a filter-codec to each subscriber. (Transmission systems had already gone digital, for example the D4 carrier system.)