Abstract: A data processing apparatus that tests whether a secure circuit is normal or not while maintaining confidentiality of the secured circuit is provided: wherein the secured circuit conducts a self-diagnostic test thereof in accordance with a self-diagnostic test start instruction signal from a CPU, and the secured circuit outputs a self-diagnostic test result signal indicating whether the secured circuit is normal or not to the CPU.

Abstract: A data processing apparatus capable of testing whether a secure circuit is normal or not while maintaining confidentiality of the secured circuit is provided: wherein the secured circuit conducts a self-diagnostic test thereof in accordance with a self-diagnostic test start instruction signal from a CPU, and the secured circuit outputs a self-diagnostic test result signal indicating whether the secured circuit is normal or not to the CPU.

Abstract: The data disc type can be discriminated in utilizing a part of control information or using through holes of disc cassette, and even in the case where the magneto-optical disc is loaded erroneously, the desired data can be recorded/reproduced on the corresponding disc selectively by shifting the operation as occasion demands. And thus, even in the case where this type of magneto-optical disc is used for data recording, the magneto-optical disc device and the magneto-optical disc which are capable of simplifying the disc control can be obtained.

Abstract: In a composite disc having a read-only area and a recordable area, user data corresponding to a map information which has been preliminarily recorded in a read-only area, is recorded to the recordable area, so that the user data corresponding to the map information can be written on the magneto-optical disc. Thereby, there can be realized a navigation system in which a large volume of user data can be reserved without a provision of a back-up power source and easiness in use is markedly improved.

Abstract: A disc having recordable and recorded areas discretely scattered over it at the same time is formed with a guard band to prevent the recorded area from being destroyed by a track jump caused by an undue impact or vibration applied to the disc during a recording operation. Additionally, storing in memory information of an edge of a recorded area by a predetermined amount before recording, the edge providing a boundary between the recorded area and a recordable area, allows recovery of data in the recorded area destroyed by a track jump caused by an undue impact or vibration applied to a disc.