Patent GB-1123055-A (GB)
Title: Digital storage system
IPC: G11B27/28
Filed: 1965-11-09
Abstract: 1,123,055. Digital data recording and processing. DIGITAL EQUIPMENT CORP. 9 Nov., 1965 [9 Nov., 1964], No. 47566/65. Heading G4C. A digital data storage and processing system comprises a record medium having a data track and a separate mark track with at least a first and a second control location in the said mark track, there being recorded in the mark track, at each of the said control locations, first and second digital control words respectively comprising such a series of digits that when the digits of the first control word are read in a forward direction and the digits of the second control word are read in the reverse direction the same first multiple-digit mark track signal results, a record reading means arranged to read from the first and second control locations when movement of the record medium relative to the reading means moves the locations therethrough and to produce a multiple-digit signal in response to each control word it reads, and a decoding means for receiving the said first mark track signal and developing at least one control signal in response thereto. Digital data record medium in the form of a tape, drum or disc comprises (Fig. 1), three data tracks 12, 14, 16, one control mark track 18 and one timing track 20. Each track is divided into 6-binary-bit frames 23, 22a, 226 &c. and the frames grouped into blocks as illustrated at the bottom of Fig. 1. Each block has six control frames in the track 18 at each end thereof the control marks at one end being the reverse complements of the corresponding control marks at the other end, whereby the same control signal may be generated irrespective of whether the record medium is moved in a forward or a reverse direction, thus facilitating searches for blocks which are identified by the digits in the end data frames 22a and 22a<SP>1</SP> (the latter being the reverse complement of the former). The codes in track 18 may be permanently recorded together with data/frames 22a, 22a<SP>1</SP>, said codes signifying amongst other things tape end (where tape is used), block start, block end and data frames. Phase modulation recording is used as shown at 20b (in which system of recording reading in the reverse direction automatically produces complements), the timing signals from track 20 being shown at 20a. Tape handling equipment for feeding data to and from a data processor 34 (Fig. 2), comprises five transducers 38a, 38b, 38c, 44 and 40 associated with the tracks 12, 14, 16, 18 and 20 respectively. Digits from control mark track 18 are fed into an 8-stage shift register 46 connected to a decoder 48 for producing control signals for a tape controller 33, the 8 bits of the register corresponding to one 6-bit frame and two bits from the preceding frame and certain of the control signals being further decoded in conjunction with a four state counter 74. A ninth stage 47 of register 46 changes from state 0 to state 1 when the first 1-bit for each block overflows from the eighth stage 46L. 18-binary digit words from the processor 34 pass via a buffer register 90 to three 6-bit reversible shift registers 92, 94, 96 for recording in corresponding frames of the three tracks 12, 14, 16. Reading is accomplished in a similar manner. When feeding tape in the reverse direction, the shift registers 92, 94, 96 are operated in the reverse direction and an inverter is included in their inputs. Blocks are selected by searching until coincidence is achieved between a block signal and the required identification word in the processor 34. A monodirectional tape feeding apparatus may be used with consequential simplification of the apparatus (e.g. shift registers).