In order to perform simultaneous recording and reproduction, a large
capacity of buffer memories were required. In addition, it was difficult
to record data while reproducing data which was recorded by a different
apparatus. The present invention has an objective of providing an
information recording medium, a simultaneous recording and reproduction
method, and an information recording and reproduction apparatus which
guarantee simultaneous recording and reproduction. The simultaneous
recording and reproduction is guaranteed by reproducing data recorded in
an area having at least a minimum size fulfilling the simultaneous
recording and reproduction condition which allows for four access
operations, recording data in an area having at least the same size, and
performing reproduction and recording alternately by switching
reproduction to recording when the data amount in the reproduction buffer
becomes full and switching recording to reproduction when the data amount
in the recording buffer becomes empty.