DATA PROTECTION SYSTEM

PURPOSE:To prevent the illegal accesses to a data area of a magnetic disk medium by using a magnetic disk controller to check the access right to the data area. CONSTITUTION:A magnetic disk monitor means 400 detects the state of a magnetic disk medium 30. If the medium 30 is kept in a usable state, an area information reading means 300 reads the data area information on the divided data areas of the medium 30 and stores them into an area information store means 200. When an input/output request is given to a magnetic disk controller 20 from an arithmetic processor 10, an access right check means 210 decides whether the input/output request can be executed or not based on the data area information stored in the means 200. If so, an access is given to the medium 30. Thus it is possible to check the access right to a magnetic disk without increasing the processing time and to protect data.