Patent GB-846493-A (GB)
Title: Digital data storage
Inventor: GERHARD DIRKS
IPC: G11B20/18
Filed: 1957-08-06
Abstract: 846,493. Checking arrangements for datastorage apparatus; reading record tapes. DIRKS, G. July 21, 1958 [Aug. 6, 1957], No. 24771/57. Class 106 (1). Apparatus for checking the accuracy as sensed of a block of data, recorded in two channels of a record medium so that one and only one signal should be read at each clock pulse from the two channels, comprises sensing means for each channel, means for generating a first error signal in response to receipt from them of simultaneous data signals, a counter operated by the data signals from both sensing means and means for testing its count after sensing of a predetermined number of data storage areas and generating a second error signal if this differs from a predetermined value. Fig. 2 shows an arrangement for recording binarycoded decimal digits received serially from 46 on to track 5 of a magnetic tape, the inversecoded form being simultaneously recorded on track 6 to facilitate detection of errors by a checking circuit 48 and a " block end marker signal " being recorded on track 7 by counter 22 at the end of (say) ten four-bit decimal digits. Clock pulses from 47 synchronous with the input pulses normally pass through gate 16 and a gate 11 or 12 to a recording head 13 or 14 according as flip-flop 10 has just been set by an input signal or not, the flip-flop being reset shortly after (delay 17) each input. Flip-flops 18-20 and gates 16 and 21 form a scale-of-five counter for the clock pulses so that each fifth clock pulse is blocked by gate 16 from the recording heads to leave a blank between each four-bit decimal digit. The checking circuit is shown in Fig. 3; heads 25 and 26 examine the tracks 5 and 6 and gate 35 provides an error signal if both simultaneously sense a bit " 1." Since one or other head transmits a pulse at each binary position, the common output of amplifiers 29 and 30 may be used as a source of clock pulses for a computer (line 45) and for an output register, gated by the sensed information from track 5 through a flip-flop 31. The clock pulses are also fed to a counter 37 which provides an output on line 51 except when it registers the correct count for the block of digits between the marker signals on track 7, so that if the count is not correct when the marker signal is sensed an erior signal will pass gate 38; the counter is reset through a delay 41. For indication of the digit or block of digits being sensed counter 37 has output lines 44 and a counter 42 is also provided : counters 22 (Fig. 2), 37 and 42 may be flip-flop counters such as disclosed in Specification 672,321. The invention is also stated to be applicable to recording on and sensing of paper tape or record cards using punched holes, or printed marks sensed by a photo-cell or of magnetic or electrically conductive ink (Specification 817,902 being referred to in this respect), and a modification is described using a magnetic drum having four pairs of parallel tracks for the four bits of each decimal digit and an error detector (all those parts of Fig. 3 within the line 52) for each track pair, the counter 37 being fed by each unit 52 through a different fractional delay circuit.