Because of the success of IBM's System 360, certain companies such as Telex entered into the marketing of devices functionally equivalent to IBM devices. The devices marketed by Telex and others plugged into and replaced parts of the System 360. In 1966 Telex began to market replacements for the magnetic tape devices which were part of IBM's System 360 computers. Before the receipt of a contract with DuPont to replace DuPont's installed second-generation IBM magnetic tape devices, Telex had been conducting engineering development work to modify the Telex Model M3000a magnetic tape drive then being marketed by Telex to other EDP equipment manufacturers to provide an appropriate electronic interface to attach to an IBM central processing unit (CPU). An interface is a shared boundary between electronic data processing machines, or more accurately between the channels or physical pathways connecting those machines, through which data or programs may be transmitted, received, stored or processed. After receipt of the DuPont contract, the work was completed and the equipment delivered in August, 1966. The Telex-developed machine was designed with an electronic interface to work in conjunction with an IBM CPU. It was designated as Telex's Model 4700. In late 1966, additional 4700's were installed at Lockheed Aircraft and at Electronic Business Service (AMI). The total engineering cost for designing the electronic interface necessary to adapt Telex's tape drive for use with IBM equipment was $42,000.