1.  Field of the Invention
The present invention relates to an information record medium having a data record area and an area for recording a directory used for managing the recorded data, and a method for recording information on such a medium. 
2.  Related Background Art
Floppy disk and magnetic hard disk which magnetically record and reproduce information, a cardshaped optical information record medium (optical card) for optically recording and reproducing information, and a disk type optical information record medium (optical disk) have been known as the information record media. 
In order to store a large amount of data on such an information record medium, auxiliary data or so-called directly for managing data block by block is used.  File information such as file names, file lengths and leading data track numbers are usually written into the directory to manage the data files. 
The optical card has a large recording capacity although it is as large as a credit card.  The size of the credit card is approximately 85 mm.times.55 mm.  Assuming that an information track pitch is 20 .mu.m and one-bit record
length is 5 .mu.m; PA1 the number of tracks is 55.times.(1000.div.20)=2750 tracks PA1 bit capacity/track is 85.times.(1000.div.5)=17000 bits PA1 byte capacity/track is 17000.div.8=2000 bytes PA1 total data capacity is 2750.times.2000=5500000 =5.5 MB
Accordingly,
In order to manage such a large amount of information, information management by the directory is essential. 
Such a directory is disclosed in U.S. patent application Ser.  No.  699,801 filed on Feb. 8, 1985 and assigned to the assignee of the present invention, and U.S. patent application Ser.  No.  064,246 filed on June 19, 1987 and also assigned to the assignee of the present invention. 
On the other hand, when data recorded on the information record medium is no longer necessary, the unnecessary data and the corresponding directory may be physically erased if the recording medium is erasable such as the magnetic disk.  However, in the optical card and optical disk, such physical erasure cannot be attained and the necessary data and unnecessary data mixedly exist on the medium.  This causes the data management complex. 
In order to solve the problem, it may be possible to irradiate a high intensity light beam on to areas in which the data and directory to be erased are recorded to destroy those areas.  However, in this method, the destroyed areas and other defect areas cannot be distinguished when the data is read.  As a result, the destroyed area may be judged as an error and the retry may be repeated.  This impedes a normal read operation.