791,216. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Sept. 27, 1955, No. 27442/55. Class 40(3). In a telecommunication exchange which automatically stores incoming messages, and retransmits the messages in accordance with destination information carried by each message, each received message is automatically directed into non-expendible storage equipment (such as a magnetic drum storage) in which alone each message is stored as a whole, and from which it is automatically transmitted over an outgoing channel. The apparatus operates in the following distinct stages:- (a) Incoming signals are received and recorded on a track on a magnetic drum. (b) The message is transferred from this track to a storage track in a common store. (c) Recordings are made showing the addresses, priority, and position in the store of the messages received. (d) Equipment chooses the message of highest priority, connects its storage track to the appropriate outgoing line tracks and transfers the message thereto. (e) The message is transmitted to line and track clearing signals are generated. The receiving circuit is shown in Figs. 17 and 18 and includes a register 181R as described in Specification 663,574. Assuming, for example, that the first three characters received are (MSMSM), (SMSMS), and (MMSMM), when the first character is received 171F is energized and the next driving pulse will step 171C and the line will be periodically examined and the information will be stored in register 181R. The first magnetic track (Fig. 21) is now set in recording motion and its mark M1 starts the transfer from register 181R to the track producing a first result, Fig. 21 (b), showing MSMSM recorded with an end indicator M2. When the second character is transferred as shown in Fig. 21 (c) an end indicator M3 appears, and finally in Fig. 21 (d) all the characters are recorded on the drum. The overall scheme of the switching centre is shown in Fig. 16. As shown, a line circuit LC starts a line-finder 23F connected to a storage selector 31F, which finds a free storage track for connection to the line track. Parallel to this operation a booking control 22F transfers signals giving the identity of the incoming lines, the priority of the message, and the identity of the common storage track on which it is recorded, to a first carrier track (1/C Carrier, Fig. 16). A free booking space on the booking track (1/C Booking Track, Fig. 16) is then hunted for and the booking information transferred to this track. All the various tracks described hitherto may be formed on separate sections of a single magnetic drum. When a message is received, the end of message character operates a storage required signal line which is picked up by common equipment for storage (marked " common store tracks " in Fig. 16) when the latter is free, and selector switches hunt for a free storage track in the pool. Each of these tracks is provided with an indicator (32F-36F) (Fig. 16), and these indicators may be brought to the free position by a track clearing signal which includes a character identifying the particular track. Means, however, are provided for examining the track periodically for untransmitted signals, and, if these are found, the indicator is returned to the engaged position. A message when transferred may take up more than one storage track. In order that the order of the message may be retained, each storage track is provided with means to mark the line track with a character corresponding to the particular track. When the next storage track is picked up, this character causes a signal identifying the second track to be returned and marked on the end of the first storage track. Thus each part of the message will bear an end character showing the track where it is continued. While the above transfer is taking place, the following booking operations are carried out. The priority, which is included at the beginning of an incoming message, is read off as the first section is transferred. The part of the common equipment which has hunted for the incoming line circuit sends a signal giving the number of this circuit. The message completed sign is read off at the end of the message and the identity of the storage track used is signalled by that part of the common equipment that makes the allocations. An intermediate unit of apparatus is provided in this connection which:- (1) Assembles the incoming line circuit number and the first storage track number and transmits them to the carrier track for booking; (2) examines all bookings regarding a particular line so that a message completed mark can be added to all bookings; (3) detects the store track number which is used. When a message that takes less than one storage track is booked, the end of message character appears before the line track is full, and is placed on the booking carrier track after the information taken from the beginning of the message. If the message requires several storage tracks, the end of message character will not appear during the transfer to the first storage track, and means must be arranged to effect a transfer before the track is completely filled. This means comprises a distributer which is energized a predetermined distance from the end of the track space. If the end of message character has not appeared when this distributer is energized, apparatus is actuated to indicate that, when the message is transferred, it is booked as an incomplete message. These transfers continue until the end of message signal is received. Hunting switches then search the booking track for bookings bearing the line track number of the message just received and give them each completion markings. Bookings are made serially in time round the booking track, blank spaces due to removal of bookings not being filled out of turn. Thus the next booking after the blank space waiting for a booking is the earliest in store. The bookings also bear markings showing their priority. A stepping pulse circuit arrangement searches the bookings in the order of their time arrival. Messages with higher priority are arranged to cut out earlier lower priority messages so that the message finally passed to a register. is the earliest message of the highest priority in the store. Means are provided for now suppressing the priority character in the message so that when the address portion is read no confusion can be caused by this character. The booking now passes to outgoing booking track 231R. At this stage all the addresses that can be reached through a single outgoing line are brought together by passing the signals through a system of multistable registers. When an outgoing line circuit is free to deal with a new message, associated apparatus is energized to conduct a search to check whether there are any bookings waiting for it, and an arrangement of registers and gates ensures that the booking with the highest priority is found. This message is then transferred to the outgoing line track (0/G Line Track, Fig. 16) and the booking erased. After a message has been received and transmitted, the various parts of the apparatus used have to be freed and track clearing signals have to be generated for this purpose. Certain elements of the storage tracks are used to indicate the number and identity of the different destinations to which a message is sent. After the message has been received and when transfer from store to an outgoing line track takes place, the related destination for the outgoing line track concerned is wiped out from the particular storage track involved. A search is continually being made of the destination elements using individual equipment for each storage track, so that, when a state is reached in which no destination elements are present, the track indicator can be set to the free condition, indicating that the storage track can be used for a further message. Specifications 713,902, [Group XL (c)], 762,094 and 790,914 also are referred to.