The technology of the optical disc has been rapidly developed and progressed as seen in CD-ROM discs (defined "ROM discs" hereinafter), encodable and erasable magneto-optical discs (defined "RAM (Random Access Memory) discs" hereinafter), etc. At the same time, efforts have been made to expand the utilization field of optical discs in accordance with the hybrid structure of ROM and RAM discs.
In the case where, for instance, image signals which are read from a ROM disc are processed to be written into a RAM disc, or voice is recorded into a RAM disc by a singer who sings a song in accordance with background music reproduced form a ROM disc, there is expected a significant advantage, if the ROM disc and the RAM disc were structured to be a single "ROM and RAM" disc.
For the purpose described above, a conventional recording and reproducing system using a recording and reproducing ROM disc and a two-light beam optical head apparatus has been proposed. One type of recording and reproducing ROM disc comprises a programmable and erasable magneto-optical region provided at an inner peripheral portion of a ROM disc. Another type of recording and reproducing ROM disc comprises a programmable and erasable magneto-optical medium film deposited on a ROM disc having rows of pits in place of an ordinary-deposited Al reflection film.
However, there is a disadvantage in the former type of conventional recording and reproducing ROM in that separate optical head apparatus are needed to be provided to independently reproduce information from rows of the pits and record and reproduce information to and from the magneto-optical region. This disadvantage leads to a complicated structure of the whole system.
In addition, there is a disadvantage in the latter type of conventional recording and reproducing ROM in that the signal light is affected by a polarized light noise caused by light reflected at the rising-up portions of adjacent pits, when a signal is reproduced from the magneto-optical medium film.