Patent GB-857284-A (GB)
Title: Improvements in magnetic recording apparatus
IPC: G06F11/14
Filed: 1957-08-12
Abstract: 857,284. Digital data storage apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 12, 1957 [Aug. 13, 1956], No. 25346/57. Class 106(1). A data storage device comprises a rotatable member having a plurality of circular magnetic recording tracks thereon, a recording head movable selectively to co-operate with different ones of said tracks, and is characterized in that the beginning of recording of each new item of data occurs at any random position along a track. In the embodiment described each new item of data comprises 60 words which is 2 words less than the capacity of each circular track and its recording is preceded by the erasure of a length of track corresponding to 4 words whereby after an item of data has been recorded its beginning and its end are separated by 2 words of erased track. The beginning and end of each item of data are further distinguished by having special characters recorded therein. As described, a number of magnetic disc data-storage units 37, Fig. 1, as described in Specification 819,789, are coupled to a general purpose computer 21 such as the I.B.M. 650 described in Specification 800,273, together with a 60-word magnetic core matrix 36 for use as a buffer store 36, as described in Specification 836,198. The computer is given three additional instructions, " seek " which causes a specified head of a specified disc storage unit to move to a specified track on a specified disc, " read " which causes all the words 60 in number in that track to be read from the track into the core buffer store and " write " which causes the contents of the core buffer store to be entered into that track. For each of these instructions the addresses of the particular head and track concerned must be registered in the distributer 34 of the computer. When a " seek " instruction becomes operative the address of the track and head are read out of the distributer under the control of a timing ring 88, decoded in a bank of thyratron latches 91 from where the addresses of the track passes to a relay register seek control unit 63 corresponding to the specified head of the specified disc store, there being one seek control unit for each head of each store. (In the preferred embodiments, ten stores each having three heads are used, giving a total of thirty seek control registers). Once the address of the required track has been transferred to the seek control relay register of the appropriate head, servo-mechanism will commence to position the head and while this is happening the computer can do other operations, in particular another address within the disc storage units can be entered into the distributer, and a further "seek" instruction can be performed so that it is possible for several heads to be moving at the same time. When a " read " instruction becomes operative, its first effect is to check that the head specified by the address in the distributer is at the track specified therein. If this is so the complete track is read into the core buffer store, and then follows immediately a check cycle during which the contents of the track are read a second time and compared with the contents of the core buffer store which are also read out simultaneously. A write instruction is similar to a read instruction. The position of the specified head is verified, writing is effected and a check cycle performed. In the case of both writing and reading, if the subsequent check cycle is not satisfactory the instruction is performed again. In the event of repeated check failures the instruction will be performed repeatedly until intervention by the operator. Form of recording and synchronization.- Data is recorded serially by bit and digit on each track in the following manner: first, Figs. 17a, 17b, an erase signal is applied to the head for the duration of four words; then data is applied serially, 60 words in all, Fig. 17c, and the speed of the disc is so arranged that this results in a final gap of 2 words, Fig. 17d. The gaps of the various discs and tracks are not aligned and each is used to locate the beginning of the block of 60 words. In order to define the gap the first digit of the first word and the last digit of the last word both have a bit recorded in their S positions, see Fig. 18, which shows digit 0 of the first word. During reading this S bit is used to turn on an oscillator A, Fig. 18, and thereafter successive data pulses cause oscillators A and B to operate alternately, there mixed outputs being used to produce clock pulses as described in Specification 837,560. Specifications 710,554 and 748,996 also, describing latch units and the non-return-to-zero magnetic recording technique, respectively, are referred to.