Patent GB-988790-A (GB)
Title: Tape error indication apparatus
IPC: G06F11/20
Filed: 1963-06-07
Abstract: 988,790. Magnetic tape stores. SPERRY RAND CORPORATION. June 7,1963 [June 20,1962], No. 22694/63. Heading G4C. Apparatus for recording and checking data on a magnetic tape comprises read heads spaced from write heads and connected to an error detection circuit which when an error is detected causes a signal pattern indicative thereof to be recorded. The arrangement described comprises a 9-channel magnetic tape having heads HD'S 1 to HD'S 9, Fig. 1b, comprising read heads "RD HEADS" and write heads "WR HEADS", each read head being spaced apart from a corresponding write head by  inch. Recording: (1) no error detected. Data to be recorded is supplied in serial form from a computer (Fig. 1d, not shown) to a line 32, Fig. 1a, and is staticized in successive groups of nine bits in a register 26, Fig. 1b, whence the data is recorded by the write heads. Each block of data 210, Fig. 2a, is followed by an "end-block pattern" 220 at the termination of which the computer supplies an "end of block insert flag" signal to a lead 34, Fig. 1a, which resets a flip-flop 18 to terminate recording in the even-numbered channels, recording of "0"s in the odd channels taking place to produce recorded area 230, Fig. 2a. The recorded data is continuously read by the read heads and when an "even channels detector" 38, Fig. 1b, senses the absence of recording in the even channels, a gate 42, Fig. 1a, is effective to cut off recording in the odd channels also. When blanks in all channels are read and detected by circuits 38, 40 an AND gate 46 supplies a signal to inform the computer than an error-free block of data has been recorded. (2) Error detected. As the recorded data is read from the tape, it is checked by an error detector 48, such as a parity check circuit, which, if it detects an error such as 214, Fig. 2b, sets an "error" flip-flop 10, Fig. 1a, thereby causing the recording of zeros in the odd channels at 230, zeros In all channels at 250, zeros in the even channels at 260, followed by blanks in all channels at 240. In addition, gate 20 is disabled to cut off the flow of data on the input lead 32. When the read heads sense the all blank area 240, the detector circuits 38, 40 cause a gate 56, Fig. 1a to provide a signal to the computer indicating that an error has been detected and an error-indicating signal pattern recorded. The computer can then re-issue the data to the tape or Indicate an error to an operator. Start pattern error. A further error detection circuit (Fig. 1c not shown) which includes a decoding matrix is effective to detect the absence of the characteristic start pattern 200, Fig. 2a, by which each block of data should be preceded thereby setting the error flip-flop 10 via an OR gate 49. Reading. At the commencement of a tape read operation, the computer applies a READ signal to one input of an AND gate 100. When an error is detected, the "error" flip-flop 10 is set as in a recording operation. If the characteristic error indication pattern 230, 250, 260, Fig. 2b is then detected, the gate 100 is opened to set a "badspot" flip-flop 102 which provides a signal to the computer to indicate that an error indication pattern has been sensed. If an error is detected thereby setting the error flip-flop 10, but no error indication pattern is sensed a gate 104 is actuated to inform the computer which can then cause the questionable block of data to be re-read.