transferred from Monarch exchange, in the City of London, on a temporary basis (via c/o switches in case something went wrong). The trial lasted from 1969 until 1970. During the development of the TXE3 it became apparent that the system would be too expensive for the competitive export market, so AEI split its team into two: one to do whatever the BPO wanted and the other to produce a reduced version for export. The trial was started in April 1968 and the model worked very well at Armour House and the BPO ordered the first half dozen exchanges. Jim Warman moved his team back from Blackheath to Woolwich to start a new department with its own manufacturing and marketing. The equipment for the first exchange had been manufactured with a 9,600 capacity and was being installed on site at Royal exchange in London in 1968 when GEC made a takeover bid for AEI. The takeover bid was successful and GEC decided that they preferred the crossbar system to TXE3 and promptly cancelled the contract to supply TXE3 to the BPO. Royal first exchange was dismantled before its installation had been completed and all the TXE3 equipment was broken up and supplied to universities for observation. Exchange description The TXE 3 exchange consists of three main areas:— Peripheral equipment comprising subscribers' line circuits, junction terminations and other units providing a variety of special functions such as coin and fee checking on coin box calls. A switching area through which connections are established between peripheral equipment. It is arranged to give three stages of switching on either side of centrally located link circuits A control area, that received information from peripheral equipment and the switching area, and processed this with data held in its own store to determine the actions required. It issued instructions to the other areas and checks their successful completion, making second attempts if necessary. The control area was called the Main Control Unit (MCU) and there were two provided on the model for security although a maximum of 12 could have been provided. Each MCU was capable of handling approximately 6,000 instructions per hour. The MCU operated in accordance with an instruction program stored in the form of a number of wires threading a bank of magnetic cores. Changes in the operating sequence can be obtained by program changes involving the re-threading of a number of wires in