Patent GB-784330-A (GB)
Title: Electronic data processing machine incorporating magnetic tape input-output device
IPC: G06F3/06
Filed: 1954-12-24
Abstract: 784,330. Electric digital-data-storage apparatus; digital electric calculating-apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 24, 1954 [Dec. 31, 1953], No. 37385/54. Class 106 (1). An electronic data processing machine comprises a calculator and a magnetic tape record input-output unit including an electrically controlled means for driving a tape through readwrite heads either forwards or backwards upon the receipt of an instruction from the calculator and coincidence switching means adapted to compare signals representing the prevailing status of the unit with signals representing the status required by an instruction and to reject, or condition the unit to accept, the instruction according to the result of the comparison. General. An electronic calculator is associated with four similar magnetic tape input-output units TU1-TU4, Fig. 1. Only the tape units and the control arrangements therefor are described in detail, the input-output circuits for transferring binary data between the tapes and a shifting register in the calculator being as described in Specification 784,155. As shown in Fig. 1, a tape unit is selected by a signal from the calculator on one of four lines such as TU1 SELECT, and further calculator instruction signals determine the function to be carried out by the selected unit. Each unit includes interlock and other control circuits whereby if the instruction is incompatible with the status of the unit a TAPE DISCONNECT signal is sent back to the calculator; otherwise, a delay is introduced while the tape motion is started or changed. For the functions (WRITE, READ, WRITE EOF) requiring forward tape motion, the TU GO FORWARD BUS is energized. Signals TAPE EOR, TAPE EOF, obtained when a tape is being read, also disconnect the tape unit from the calculator. The control circuits consist primarily of electromagnetic relays and standard units (circuit diagrams given) including double triode trigger circuits and AND and OR diode circuits. The construction of a tape unit and the five calculatorcontrolled functions are described separately below. Magnetic tape unit. The tape 14, Fig. 2, extends between a " file " reel 10 and " machine " reel 18 whose spindles 12, 20 may be selectively driven in either direction, the tape passing over idler roller 10a into column 24, over movable idler 32, through read/record head assembly 16, and via movable idler 34 to column 26 and idler 18a. The columns 24, 26 each comprise an air-tight casing the width of a tape, in which a tape loop fits so that its bight contacts the side walls as shown to form an air seal, and the space below each loop is evacuated by a vacuum pump 110. The tape reels are so controlled that the loops are maintained between upper and lower vacuum switches LUV, LLV or RUV, RLV. The reel spindles are driven through electromagnetic clutches from two motors (not shown) which continuously drive belts 22a, 23a, Fig. 4, respectively in opposite direction, belt 22a for example driving the reeling clutch 44 for reel 10 and the unreeling clutch 50 for reel 18. If, e.g., the switch LLV, becomes subject to atmospheric pressure owing to the loop in column 24 dropping below it, it operates the reeling clutch 44 to shorten the loop, and similarly if switch LOV becomes subject to a vacuum owing to the loop rising above it, it operates unreeling clutch 46. When a loop is between its associated switches, contacts of the latter energize an electromagnetic brake 42 or 48, Fig. 4, similar to the clutches except that the reel spindle is coupled to a stationary shell. The tape is driven through the head assembly 16 by a motor (not shown) which constantly drives capstans 28, 30, Figs. 2 and 6, in opposite directions. Movable idlers 32, 34 are connected by linkwork including lever 140, 142, 144 whereby they may be selectively engaged with a drive capstan, or an associated stop capstan 36 or 38. The lever 144 is connected to an armature 154 controlled by forward and backward bias relays 146b and 146a respectively, and via a rod 158 to moving coil 150 of a stop-go clutch device 148 comprising also a permanent magnet 152. In the position shown in Fig. 6, relay 146b is energized to attract armature 154, and coil 150 is so energized as to be repelled from magnet 152, whereby a rightward and upward thrust is imparted to lever 144 which causes idler 34 to be engaged with capstan 30; tape is then pulled through the head in the forward direction (from reel 10 to reel 18). To stop the forward drive, the current through coil 150 is reversed so that the coil is attracted by 152 thus moving lever 144 downward and raising both idlers 32, 34 the former then engaging the forward stop capstan 36. Similarly, when relay 146a is energized, tape is driven backward or is stopped by engagement between 32 and 28 or 34 and 38 respectively. Means for damping the motion of the coil 150 and associated mechanism are discussed. The tape is attached to the reels 10, 18 by short and long metal leaders respectively, both long enough to reach from the appropriate reel to idler l0a ; this facilitates tape-loading and unloading when a fine reel is changed, and enables the end of a tape to be sensed. Various manual controls for the tape unit are provided. Tape writing. The SET TU WRITE STATUS signal, Fig. 1, is applied to " Disconnect " circuits (not shown) which, if a tape unit is in the " read status " as indicated by the output of a trigger circuit 365, Fig. 43, apply a TAPE DISCONNECT signal, Fig. 1, to the calculator. Provided the " read status " trigger 365 has not been operated, the SELECT STOPPED TU signal for the selected tape unit allows the WRITE STATUS signal to pass through AND circuit 484 and set the " write status " trigger 366 via cathode follower 490. The output of 484 is sent also to tape motion control circuits (Fig. 45, not shown) which introduce delays according to the status of the tape, before the write operation can begin; if a " direction status " trigger (Fig. 15, not shown), which controls relays 146a, 146b, indicates that the tape drive is in forward status, a GO signal is applied to coil 150, Fig. 6, and a "starting delay " is introduced (by a single shot multivibrator) to allow time for the tape to be brought up to speed; if the tape drive is in backward status, a further prior " changing delay " is introducedduring which the direction status " trigger is changed to the " forward " condition. The tape unit may not accept a new calculator instruction until after it is stopped at the end of a writing operation. Tape reading. The SET TU READ STATUS signal, Fig. 1, like the WRITE STATUS signal, is applied to the Disconnect circuits, a TAPE DISCONNECT signal being obtained if the selected tape unit is in the " write status." Otherwise, the READ STATUS signal passes through AND circuit 566, Fig. 43, to AND circuit 568, and to the tape motion control circuits to test for tape status, as during writing, and to introduce delays as necessary. The " starting delay " signal passes through circuit 568 to set the " read status " trigger 365. If, after reading information., no information pulses are received from the tape for a predetermined period, an " end-of record " signal is produced (by single-shot multivibrators) which stops the tape, a signal TAPE EOR, Fig. 1, then causing the tape unit to be disconnected from the calculator. If no information is received for a longer predetermined period after the tape has been started, indicating an " end of file," similar operations are performed, a signal TAPE EOF being sent to the calculator. Reading backward. The TU READ BACKWARD signal, Fig. 1, produces the same operations as in forward read, described above, except that the tape motion control circuits are arranged to give backward motion to the tape. Tape rewinding. The SET TU REWIND STATUS signal, Fig. 1, causes the tape motion control circuits to change the tape drive to backward status (if not already in it). The signal then passes through AND circuit 362, Fig. 43, to produce a REWIND-DISCONNECT signal which resets the read and write status triggers 365 and 366 via OR circuit 368, and generates a TAPE DISCONNECT signal, Fig. 1, so that the calculator can proceed without waiting for the rewinding operation. The tape drive is initiated and the tape is rewound until the long metal leader earths idler 18a, Fig. 2, when a signal is obtained which stops the tape and prepares the tape unit for accepting another calculator instruction. Writing end-of-file. The SET TU WRITE EOF STATUS signal, Fig. 1, causes a SET TU WRITE STATUS signal to be produced which, as during Writing, described above, is applied to the Disconnect circuits, and to AND circuit 484, Fig. 43, to set the write status trigger 366 provided the selected tape unit is not in read status. As soon as the tape drive is in forward status, the WRITE EOF signal passes through AND circuit 548 to set a write EOF status trigger 552 and to provide a TAPE DISCONNECT signal. The tape drive is started and zeros are written on the tape continuously during a " write EOF delay "; an END WRITE EOF signal then stops the tape and passes through OR circuit 368 to reset the triggers 365, 366, trigger 552 being reset by the trailing edge of a TAPE UP TO SPEED signal. The tape unit is thus reset to " neutral."