Patent ID: RE42826

Claim:
A rewritable optical disk of which recording area is divided into a plurality of groups arranged from an inner group to an outer group and having annular boundaries; the number of sectors per track differing from one group to another, said optical disk having a spare area associated with each of said groups and having sectors which can be allocated in place of defective sectors of the disk; wherein a control data area holding information for controlling recording/reproducing operation from said optical disk, a plurality of defect management areas holding information for controlling replacement of defective sectors, and said control data area contains position information recorded to indicate the positions of at least one of said defect management areas, said spare area having a size that may be varied as needed; the total space occupied by said recording area and spare area being substantially constant so that reducing the size of said spare area increases the size of said recording area, and the ratio of the spare area to recording area being greater in one of said inner and said outer group than in other of said plurality of groups.