Optical disc recording and/or reproducing apparatus having a buffer memory to accommodate track jumps

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The following are the specifications for a disc-shaped recording medium according to the present invention, referred to hereinafter as a disc.
Referring to FIG.
1A, the disc 1 has an outer diameter D equal to 64 mm, a center hole diameter d equal to 10 mm and a signal recording area W, shown by hatching, of a diameter of 32 mm or more.
The disc 1 has a thickness t which, as shown in FIG.
1B, is equal to 1.
2 mm.
A recording track is formed spirally on the disc 1 at a track pitch of 1.
6 .
mu.
m.
The disc 1 is driven rotationally at a constant linear velocity of 1.
2 to 1.
4 m/s.
In the present embodiment, information of 130M bytes or more may be recorded by compression of the information for recording.
For example, when audio signals undergo analog to digital conversion at a sampling frequency of say 44.
1 kHz on the 16-bit-per-sample basis, 2-channel audio data of 60 minutes or longer may be recorded and/or reproduced by compressing the digital audio data at a compression rate of e.
g.
1/4.
For the present embodiment, two different disc types may be contemplated.
The present embodiment provides a reproduce-only optical disc, on which signals are recorded by a train of pits produced by injection molding or the like, and an overwrite type magneto-optical disc having a photomagnetic recording layer for recording, reproduction and erasure.
The reproduce-only optical disc includes a transparent disc base plate of polycarbonate or PMMA, on which information signals, herein digital audio signals in the form of a train of pits, have been transferred by injection molding from a pattern of projections and valleys of a stamper consistent with the information signals.
A reflecting film of a metal, such as aluminum, is deposited on the surface of the recording layer, such as by vacuum deposition or sputtering, and a protective layer of an UV resin or the like is applied on the reflective layer, such as by spin coating.
The overwritable magneto-optical disc includes a disc base plate of a transparent plastic material, such as polycarbonate or PMMA, on which a photomagnetic recording film (perpendicular magnetization film) of, for example, TbFeCo, is deposited, such as by vacuum deposition or sputtering, and a protective film of, for example, UV resin, is deposited thereon