There has been known a magnetic disc, a so-called floppy disc, which comprises magnetic layers formed on opposite sides of a flexible disc base of a polyester sheet or the like. Information is recorded on the floppy disc by a magnetic head while rotating the floppy disc at high speed. Such floppy discs have been mainly used as recording media for computers because they are easy to handle and can be produced at low cost.
Recently the magnetic disc of this type is generally held for rotation in a small hard casing and used in the form of a magnetic disc cartridge as represented by a 3.5-inch floppy disc.
In the magnetic disc cartridge with a hard casing, the casing is provided with an opening for giving a magnetic head access to the magnetic disc therein and the opening is normally closed by a shutter urged in one direction so that foreign matters such as dust cannot enter the casing.
There has been constant demand for a magnetic disc cartridge having a larger storage capacity and 3.5-inch floppy discs having a storage capacity of 1 MB or 2 MB have been put into practice. Further even 3.5-inch floppy discs having a storage capacity of not smaller than 100 MB have been provided.
When a magnetic disc cartridge larger than conventional magnetic disc cartridges in storage capacity is developed, a novel disc drive system for driving the magnetic disc cartridge having a larger storage capacity is sometimes provided. Such a novel disc drive system is generally arranged to be able to drive magnetic disc cartridges having smaller storage capacities as well as the newly developed larger capacity magnetic disc cartridge. Such capability of driving magnetic disc cartridges having smaller storage capacities as well as the newly developed larger capacity magnetic disc cartridge will be referred to as "downward compatibilities", hereinbelow.
In order to provide a disc drive system with such downward compatibilities, the newly developed larger capacity magnetic disc cartridge should be substantially the same as the conventional magnetic disc cartridges in appearance and the like. Accordingly, there is fear that the newly developed larger capacity magnetic disc cartridge is loaded in a disc drive system for the conventional smaller capacity magnetic disc cartridges. The disc drive system for the conventional smaller capacity magnetic disc cartridges will be referred to as "smaller-disc drive system" and the disc drive system for newly developed larger capacity magnetic disc cartridges will be referred to as "larger-disc drive system", hereinbelow.
Generally the smaller-disc drive system is not provided with function for satisfactorily protecting the newly developed larger capacity magnetic disc cartridge, and when the disc drive system is operated loaded with the newly developed large capacity magnetic disc cartridge, information stored in the magnetic disc can be destroyed.
Though accidental recording or erasure can be prevented by providing, for instance, a hole for distinguishing the storage capacity on cartridges, when a larger capacity magnetic disc cartridge is accidentally loaded in a smaller-disc drive system and a magnetic head of the smaller disc drive system is brought into contact with the magnetic disc medium in the magnetic disc cartridge, there is fear that foreign matters or dust on the magnetic head adhere to the magnetic disc medium.
Since the larger capacity magnetic disc is obtained by increasing the recording density, the recording wavelength is shorter and the recording track is narrower. Accordingly when foreign matters are on the larger capacity magnetic disc medium, errors can be generated in reading out recorded data.
In view of the foregoing observations and description, the primary object of the present invention is to provide a larger capacity magnetic disc cartridge which cannot be loaded in a disc drive system exclusively for a magnetic disc cartridge having a smaller storage capacity.
Another object of the present invention is to provide a disc drive system for larger capacity magnetic disc cartridges.