1. Field of the Invention
The present invention relates to an optical disk such as an optomagnetic disk formatted in a disk manufacturing process, a disk drive unit for performing a seek operation of the optical disk formatted in the manufacturing process, and a system having the optical disk and the disk drive unit.
2. Related Background Art
A conventional disk of the aforementioned type is formatted with specific data by a manufacturer during the disk manufacturing process, and tracks are divided in units of sectors.
A data format of an optical disk in the conventional manufacturing process is shown in FIG. 5.
Referring to FIG. 5, a track 19 includes sectors 20. In an enlarged view, each sector 20 is constituted by a sector mark 21 representing a start position of the sector, an ID portion 22 for storing a track address and a sector address, and a data portion 23 for storing user data.
In formatting during the manufacturing process, the sector mark 21 and the ID portion 22 of each sector 20 are written on the disk.
A disk drive unit for driving an optical disk formatted during the manufacturing process is designed to access sectors designated for reading/writing user data, i.e., to perform the following two operations:
(a) seek operation for moving a head to a track including the designated sector; and PA1 (b) search operation for searching for a designated sector within the track after the seek operation is performed. PA1 seek operation for moving the head to the track including the designated sector; PA1 operation for searching for the designated sector within the track after the seek operation is completed; PA1 operation for accessing the data portion and transferring read-out data to the host; and PA1 operation for writing the formatted user data in the data portion.
To control the seek operation, a track address signal as described above is always read out during the seek operation to detect a radial position of the head.
In the search operation performed upon completion of the seek operation, sector address signals of the sectors within the track are sequentially read out to find the designated sector.
The disk drive unit for driving the optical disk formatted in the conventional manufacturing process must have an address signal reader function conforming with the disk format (i.e., a sector mark is detected, and then the address signal is read out from the ID portion after detection of the sector mark).
In addition, the conventional optical disk drive unit has a disk controller function for writing user data in the sector accessed in accordance with a specific format, and for reading out data in accordance with the write format.
The formats of some conventional optical disks are determined by manufacturers. If a user wants to change a format so as to change the number of data stored in one sector or the like, he cannot easily change do so.
In order to overcome the above inconvenience, a manufacturer may not format a disk at all, so that the user can freely format the disk. In this case, nonformatted disks are supplied to users.
In the case of nonformatted disks, since the user's format is unknown, a disk drive unit cannot incorporate a function for reading out an address signal, a function for formatting user data in a form to cause the user data to be written in the data portion, a function for accessing the data portion in accordance with the format, and a function for controlling a read/write access. A circuit having these functions must be developed as a disk controller by a user or by a joint development between the user and the manufacturer.
Therefore, the disk drive unit and disk controller must be two independent units.
In this case, the disk drive unit has only a function for writing a signal transferred from a disk controller on the basis of a write instruction from the disk controller, a function for reading out a signal from the disk in accordance with a read instruction and for transferring the read-out signal to the disk controller, and a function for moving the head to the designated track on the basis of information from the disk controller.
The disk drive unit alone cannot perform the following operations for reading out user data:
As described above, seek control is always performed on the basis of the track address signal written in the ID portion of the sectors. Therefore, in order to allow a user to freely format data, the function for reading out the address signal must be incorporated in the disk controller.
The disk drive unit always transfers a signal read out from the disk to the disk controller during a seek operation. The disk drive unit causes the disk controller to read the track address signal from the transferred signal, and the address signal must be fed back to the disk drive unit, thereby controlling the seek operation.
In searching for the designated sector upon completion of the seek operation, the disk drive unit reads out the signal from the disk upon completion of the seek operation and transfers the read-out data to the disk controller. The address signal of each sector is read by the disk controller from the signal transferred from the disk drive unit and is then fed back to the disk drive unit, thereby causing the disk drive unit to find the designated sector on the basis of the fed-back address signal.
Signal transfer is also used to read/write access the data portion. After the designated sector is searched, the disk drive unit reads out a signal from the data portion in accordance with a read instruction from the disk controller and transfers the read-out signal to the disk controller. The disk drive unit writes a signal transferred from the disk controller in the data portion in accordance with a write instruction sent from the disk controller.
In the nonformatted disk system just described, because the disk controller and the disk drive unit must be independent units, as noted earlier, the track address signals required in control of a seek operation must be transferred from the disk controller to the disk drive unit through an interface circuit. As a result, a time required for a seek operation is increased, and the seek capacity is undesirably degraded.