Multisystem network, and device and method for access to data storage

A device for access to a data storage unit, comprising:

• a data storage unit having a data storage area including first and second areas different from each other;
• a first processor capable of direct access to the data storage unit, the first processor including a first file descriptor management table;
• a first buffer that is controlled by the first processor to read data from or write data to the first area of the data storage unit and holds the data;
• a register that stores a command or control data used for the first processor to access the data storage unit and an emulation register corresponding to the register;
• a second processor capable of access to the data storage unit via the emulation register and with intervention of the first processor, the second processor including a second file descriptor management table and a file descriptor correspondence table;
• a second buffer that is controlled by the second processor to read data from or write data to the second area of the data storage unit and holds the data;
• and
• a selecting means that is controlled by the first processor to select data from either the first or second buffer as data to be read from or written to the data storage unit,
• wherein the first file descriptor management table is a file system to manage data read from or written to the data storage unit,
• wherein file descriptors issued by the first and second devices are managed by the first and second file descriptor management tables respectively, a correspondence relationship between the file descriptors is stored in the file descriptor correspondence table.

A method for accessing a data storage unit by a first device including a first processor and a second device including a second processor, the first processor including a first file descriptor management table and the second processor including a second file descriptor management table and a file descriptor correspondence table, comprising the steps of:

• dividing a data storage area of the data storage unit into a first area used for the first device and a second area used for the second device;
• providing an emulation register corresponding to a register which gives priority to data read and write, by the first processor, from and to the first area of the data storage unit and stores a command or control data used for access by the first processor to the data storage unit;
• providing data transfer between the first device and data storage unit through direct access by the first processor to the data storage unit via the connection circuit;
• and
• providing data transfer between the second device and data storage unit through access by the second processor to the emulation register and access, corresponding to the content of the emulation register, by the first processor to the data storage unit,
• wherein the first file descriptor management table is a file system to manage data read from or written to the data storage unit,
• wherein file descriptors issued by the first and second devices are managed by the first and second file descriptor management tables respectively, a correspondence relationship between the file descriptors is stored in the file descriptor correspondence table.

A device for access to a data storage unit, comprising:

• a data storage unit having a data storage area including first and second areas different from each other;
• a first processor capable of direct access to the data storage unit, the first processor including a first file descriptor management table;
• a first buffer that is controlled by the first processor to read data from or write data to the first area of the data storage unit and holds the data;
• a register that stores a command or control data used for the first processor to access the data storage unit and an emulation register corresponding to the register;
• a second processor capable of access to the data storage unit via the emulation register and with intervention of the first processor, the second processor including a second file descriptor management table and a file descriptor correspondence table;
• a second buffer that is controlled by the second processor to read data from or write data to the second area of the data storage unit and holds the data;
• and
• a selector that is controlled by the first processor to select data from either the first or second buffer as data to be read from or written to the data storage unit,
• wherein the first file descriptor management table is a file system to manage data read from or written to the data storage unit,
• wherein file descriptors issued by the first and second devices are managed by the first and second file descriptor management tables respectively, a correspondence relationship between the file descriptors is stored in the file descriptor correspondence table.