PROTECTION SYSTEM FOR DELETION DATA SECRECY

PURPOSE:To prevent illegal reading by initializing all table indications in a space area to old data indication states when assigning the space area for a data set, and setting corresponding positions to new data indications when data are updated by the subsequent writing processing of new data records. CONSTITUTION:A command analysis part 8 analyzes a command supplied from a CHU4, and actuates processing parts 9-11 respectively when the command is a purge, read, or write command. Consequently, a data purge processing part 9 sets the indication of a position CCHH corresponding to the destination in a purge control table to an ON state. A reading processing part 10 refers to said indication (ON) to set a purge bit 12a provided to a sense byte 12 to ON, and turns on a unit check signal UC to cause an interruption to the CHU4. The CHU4 accepts it and informs a CPU1 that a read inhibition state is now set by purging.