Patent Number: 
Section: claims

1. An optical storage medium, comprising stacked data storage layers each of which is readable/writeable separately from the other layers by means of a light beam striking one side of the optical storage medium, whereina recordable area of a first data storage layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which the first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of the second data storage layer, and, further, whereinsaid first data storage layer is located closest to a light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer, away from said light-striking surface. 2. The optical storage medium as set forth in claim 1,whereinat least one of said at least one extended area portion is a pseudo-recording area which is fully prerecorded. 3. The optical storage medium as set forth in claim 2,whereinsaid pseudo-recording area stores identification information which is unique to said optical storage medium and by which said optical storage medium is distinguished from other optical storage media. 4. The optical storage medium as set forth in claim 3,whereininformation in said pseudo-recording area is not rewriteable. 5. The optical storage medium as set forth in claim 2,whereinsaid pseudo-recording area stores encryption information by which data are encrypted before being recorded on said optical storage medium. 6. The optical storage medium as set forth in claim 5,whereininformation in said pseudo-recording area is not rewriteable. 7. The optical storage medium as set forth in claim 1,whereinsaid data storage layers exhibit a lower optical reflectance in recorded areas than in non-recorded areas. 8. The optical read/write apparatus as set forth in claim 1, whereina recordable extended area portion is provided adjacent to each end of a main recordable area portion of said first data storage layer, so as to cover more than the area directly above said recordable area of said second data storage layer in the direction in which said first and second data storage layers are stacked. 9. The optical read/write apparatus as set forth in claim 1, whereina recordable extended area portion at one or more ends of a main recordable area portion of said first data storage layer extends into one of the group consisting of an innermost part of said first data storage layer, an outermost part of said first data storage layer, or an address area on said first data storage layer. 10. The optical read/write apparatus as set forth in claim 9, whereina recordable extended area portion at one or more ends of said main recordable area portion of said first data storage layer extends into a region having a lower optical transmittance than said main recordable area portion of said first data storage layer. 11. The optical read/write apparatus as set forth in claim 9, whereina recordable extended area portion at one or more ends of said main recordable area portion of said first data storage layer extends into a region having a higher transmittance than said main recordable area portion of said first data storage layer. 12. The optical storage medium as set forth in claim 1, whereinat least one of said at least one extended area portion is assigned as a test write area. 13. An optical read/write apparatus, comprising:illumination means for supplying a read/write light beam;optical storage medium mounting means for supporting an optical storage medium such that said read/write beam from said illuminating means strikes only a light-striking side of said optical storage medium,said optical storage medium including stacked data storage layers each of which is readable/writeable separately from the other layers by means of a light beam striking said light-striking side of said optical storage medium, wherein:said optical storage medium is structured and configured such that a recordable area of a first data storage layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which the first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of the second data storage layer, and, further, whereinsaid first data storage layer is located closest to said light-striking surface of said optical storage medium, and the second data storage layer is located next to the first data storage layer, away from said light-striking surface; and whereincontrolling means controls said illuminating means so that at least one of said at least one recordable extended area portion of said optical storage medium is fully recorded first. 14. The optical read/write apparatus as set forth in claim 13, whereinsaid optical storage medium exhibits a lower optical reflectance in recorded areas of said data storage layers than in non-recorded areas thereof. 15. An optical read/write apparatus comprising:illumination means for supplying a read/write light beam; andoptical storage medium mounting means for supporting an optical storage medium such that said read/write beam strikes one side of an optical storage medium, said optical storage medium including stacked data storage layers each of which is readable/writeable separately from the other layers by means of said light beam striking said one side of said optical storage medium, wherein:said optical storage medium is structured and configured such that a recordable area of a first data storage layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which said first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of said second data storage layer, and, further, wherein said first data storage layer is located closest to a light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer, away from said light-striking surface; and wherein controlling means controls said illuminating means so as to write test data in at least one of said at least one extended area portion. 16. The optical read/write apparatus as set forth in claim 15, whereinsaid optical storage medium exhibits a lower optical reflectance in recorded areas of said data storage layers than in non-recorded areas thereof. 17. An optical read/write method comprising the steps of:providing a read/write apparatus comprising:illumination means for supplying a read/write beam; andoptical storage medium mounting means for supporting an optical storage medium such that said read/write beam from said illumination means strikes only a light-striking side of said optical storage medium, said optical storage medium including stacked data storage layers that each are readable/writable separately from the other layers by means of a light beam striking said light-striking side of said optical storage medium, wherein said optical storage medium is structured and configured such that a recordable area of a first layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which said first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of said second storage layer, and further wherein said first data storage layer is located closest to said light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer away from said light-striking surface; and wherein control means controls said illuminating means so that at least one of said at least one recordable area portion of said first layer of said optical storage medium may be fully recorded first; andfully recording said at least one of said at least one extended area portion first. 18. An optical read/write method comprising the steps of:providing a read/write apparatus comprising:illumination means for supplying a read/write beam; andoptical storage medium mounting means for supporting an optical storage medium such that said read/write beam from said illumination means strikes only a light-striking side of said optical storage medium, said optical storage medium including stacked data storage layers that each are readable/writable separately from the other layers by means of a light beam striking said light-striking side of said optical storage medium, wherein said optical storage medium is structured and configured such that a recordable area of a first layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which said first and second data storage layers are stacked, and at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of said second storage layer, and further wherein said first data storage layer is located closest to said light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer away from said light-striking surface: and wherein control means controls said illuminating means so as to write test data in at least one of said at least one extrended area portion first; andwriting test data in said at least one of said at least one extended area portion first.