INFORMATION PROCESSOR

PURPOSE:To inhibit a medium from being read by a device except a device which is used for writing by writing characteristic information on the medium, device by device, automatically and performing collating operation automatically at the time of reading. CONSTITUTION:For example, when a floppy disk medium 1 is formatted on a device, whether or not device switch information is written on the medium can be selected and when the writing is specified here, the contents of a device switch 2 are written at a certain specific part 3, e.g. a characteristic sector on the 0 cylinder after the formatting operation. In this case, information on each device user is written additionally to information in the device switch 2 and the added information is recorded and held in the device switch 2 as well. When the floppy disk medium 1 is loaded on the device, its medium information is read in and when the information is not the initial value data after the formatting, it is compared with the information in the device switch to disable following processing unless the information is coincident. Consequently, the medium can not be read except by the device which is used at the time of the writing.