that is as shown in fig2 a 2b 2 c and 2 d the sound groups sg 00 to sg 0 a are comprised in two consecutive sectors made up of an even sector such as sector s 00 and an odd sector such as sector s 01 each sound group is made up of 424 bytes and corresponds to the sound data volume corresponding to 11 61 msec referring to fig2 e data are recorded in l and r channels within one sound group sg as shown in fig2 e for example the sound group sg 00 is made up of l channel data l 0 and r channel data r 0 whilst the sound group sg 01 is made up of l channel data l 1 and r channel data r 1 meanwhile 212 bytes which become the data area of the l r channel are called a sound frame the cluster format explained in fig2 a 2b 2 c and 2 d is formed in the entire area of the magneto optical disc 90 which is divided in the radial direction into a radially inner area as a management area and into a program area contiguous to the management area in the radially inner disc area there is provided a replay.