| 摘要 |
PROBLEM TO BE SOLVED: To inhibit the use of CD-ROM which is illegally copied by judging the error rate of data which is read from CD-ROM. SOLUTION: Key code data which a bit read part 2 reads is errorcorrected by an error correction part 3 and is transferred to the error rate comparison part of a judgment part 4 by a key code data extraction part 7. The error rate comparison part checks the number of corrected key code data and the number of key code data which cannot be corrected among transferred key code data. The total number is divided by all the number of key code data so as to obtain the error rate Q. Since the error rate K is given to key code data in legal CD-ROM, the error rate Q is compared with the error rate K, When it becomes Q≈K, the CD-ROM is legal. When it is judged to be legal as the result of judgment, a bit read control part gives the indication of the reading of user data to the bit read part 2. |
