Patent GB-1479861-A (GB)
Title: Elongate magnetic record tape
IPC: G11B27/32
Filed: 1975-02-28
Abstract: 1479861 Magnetic tape recording format INTERNATIONAL BUSINESS MACHINES CORP 28 Feb 1975 [14 March 1974] 8382/75 Heading G5R A magnetic record tape, intended for reading and writing digital data in data tracks 21, 22, Fig. 2, inclined to the tape edges 30, 33 and scannable by a transducer movable in a path at the same angle to the tape edges, includes longitudinal servo track areas 17, 19 adjacent edges 33, 30 respectively and each containing recorded sensable indicia indicative of the intended alignment of the transducer with each said data track, and a longitudinal address track 25 between tape edge 30 and servo track area 19 and containing recorded sensible indicia indicative of an address for each data track, the servo track area 19 and the address track 25 being within an area whose edge is less than one fourth of the width of the tape from the edge 30. Such area preferably has a width of only one sixth the tape width. Each of the servo track areas 17, 19 may have two parallel tracks or only a single track. The tape has a tapered leading end (12), Fig. 1 (not shown) to facilitate autothreading and is wound on a single-flange reel (10) having a cover for storage as disclosed in Specification 1,416,069, the cover being transparent for reading of tape-identifying indicia (13) which are repeated in a first said data track (0). The data tracks 21, 22 &c. extend at 17¢ degrees to the tape edges and are preceded by a test area (15) in which are recorded data indicating the differences in terms of data track width, spacing &c. between the tape and a standard, area (15) including further signals by which the amplitude, phase shift and other characteristics of the readback signal are analysed for automatic optimum setting of the playback circuits. To provide for re-recording of the data tracks without error, to overcome problems of mechanical differences between recorders, the data tracks are grouped into blocks (110), (111), separated by areas (112) with no recordings and equivalent to an area of one or two data tracks. The address track 25 has parallelogram areas each corresponding to a respective data track; each such area may be six mils. long with four mil. gaps between areas. The data tracks 21, 22 &c. may be contiguous with one another. Recording apparatus, Fig. 4, for such a tape has a helical scanner comprising a rotor 62 between stationary mandrels 60, 61 and carrying write and read heads with gaps W, R to scan along paths 27, Fig. 2, while the tape 11 is stationary. The position of the gaps W, R along path 27 is indicated by outputs 80, 81, 82 from a counter 74 counting signals from a detector 75 sensing marks around a disc 71 rotating with rotor 62, counter 74 being reset when detector 73 senses a mark 72 on disc 71 aligned with gaps W, R. The write gap W has a width about twice that of read gap R and is used to record address track 25 as well as the data tracks. The gaps W, R are spaced apart along path 27 by a distance slightly longer than the width along path 27 of each of servo areas 17, 19 so that at the start of a scan as the read head reads the address track 25, the write head reads servo area 19 to supply signals to a servomechanism to accurately align the path 27 with the chosen data track. If the signals read off address track 25 indicate that the tape is appropriately positioned a computer passes data signals to be recorded in area 16 to the write head via circuits 84 and an AND circuit 85 enabled by an output 80 of counter 74 only when the write head is scanning area 16. The read head check-reads the data track so recorded at the end of a scan along path 27 the write head reads servo area 17 and the resultant signals are used for tape positioning the tape is then stepped to the next desired data track by reel motors 102, 104 under the control of positioning control 100 having inputs from detectors 73, 75, the computer, servo circuits 90 receiving signals from the write head when reading servo areas 17, 19, and a tachometer 105 supplying take-up reel position data signals converted by the computer to linear tape position data.