Patent GB-883461-A (GB)
Title: Improvements in or relating to magnetic recording systems
Inventor: KILBURN TOM
IPC: G11B20/16
Filed: 1958-01-14
Abstract: 883,461. Electrical digital data-recording apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Jan. 9, 1959 [Jan. 14, 1958], No. 1307/58. Class 106 (1). Apparatus for checking information as it is recorded on a magnetic drum comprises means for recording an element of the information, means for reading the element and means for applying immediately to the said recording means an indication as to whether the element read satisfies the test. The invention is applied to the apparatus described in Specification 786,734. A combined read-write head is shown in Fig. 1. The writing coil WL is effective while the associated magnetic tape is moving, the reading coil RL while the tape is substantially stationary. Alternating current is fed to coil ML so that any signal picked up from the tape modulates the A.C. read out by coil RL. Assuming that magnetic tape control flip-flop 1, Fig. 3a, is off output instructions from the computer are applied to the tape staticizers (not shown). A pulse on terminal 2 sets flipflop 1 to on to start the tape moving and to start up a waveform α which sets staticizers I0-I6 to 1. It also energizes element 5 to generate a clamp waveform CL of 300 Ásecs. duration. A waveform # the inverse of α, together with information signals INV (Q0-Q6), sets the I staticizers and energizes writing heads W0-W7, according to 5 bits of output information and a parity digit, a check digit being applied to I5 and W5, W6. The trailing edge of the a waveform is used, Fig. 3b, to examine the combined outputs of the I staticizers and the information signals INV (Q0-Q6). In the event of a discrepancy flip-flop 11 is set to operate an alarm and stop further operation by resetting flip-flop 1, Fig. 3a. Flip-flop 11 is also set if there is failure to read both check tracks 5 and 6. After the writing operation clamp waveform CL ends and the tape moves the recorded digits under reading heads R0-R7. The output signals r0-r7 produce a clock waveform CLO (Fig. 3c, not shown) to produce 10 Ásec. pulses hO, h1 (Fig. 3d, not shown). Output signals r0-r7 also operate gates to set the I staticizers, the check digit being double-recorded in 15 as a safety measure. The outputs of the I statizers are mixed, Fig. 3e, and gated at 19 by pulse hO before being fed to a flip-flop 20. If the information has been correctly recorded, all the I staticizer outputs are positive and flipflop 20 remains in normal condition. In the event of one or more errors, flip-flop 20 is operated at the time of pulse hO and remains operated until recording is effected correctly. Error is indicated by pulsing lead INV CH to make an error mark in the next recording interval. If flip-flop 20 indicates correct operation the next h1 pulse restores the magnetic tape control flip-flop 1, Fig. 3a, to stop condition so that the sequence of operations corresponding to the next instruction in the computer may proceed. If incorrect operation is indicated then the pulse h1 initiates new α and # waveforms and the whole sequence is repeated to re-record the previously incorrectly recorded information. Details. The parity signal INV Q6 is 1 or 0 according to whether the sum of the binary digits in INV Q(0-4) is even or odd, so that the gross sum must be even for correct operation. Failure in both check tracks at the same digit position stops the system.