Importance

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Abstract

In an optically readable information recording disc (D), a spiral guide track (T1) is formed in the form of geometrical variations to provide not only a tracking signal (Sc) but also synchronous signals (Sb, Sr) and cumulative time data (St) which varies depending on the place in the recording layer of the disc. This spiral guide track, which is referred to as ROM track, is formed when a disc is manufactured by stamping and the information uneraseably written in the guide track is read during recording and reproducing main information which is written and read out on and from another sprial track (T2) or land portion formed between two adjacent spiral guide tracks. This spiral track used for recording/reproducing main information is referred to as RAM track. The recording layer of the disc having the ROM track (T1) and RAM track (T2) is divided into a lead-in signal area (2), a lead-out signal area (4) and a main signal recording area (3) interposed between the former two areas, so that necessary lead-in signal and lead-out signal are respectively written in corresponding areas. The RAM track and two ROM tracks at both sides of the RAM track are simultaneously scanned by three laser light spots (Lb1, Lb2, Lb3) so that tracking information is read out from the two ROM tracks and synchronous signal and cumulative time data are read out from one of the two ROM tracks while main information is either written or read out on and from the RAM track.

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First Claim