APPARATUS AND METHOD FOR
RANDOMLY ACCESSING SEQUENTIAL
BACKGROUND OF THE INVENTION
The present invention relates to an information storage device and, in particular, to an information storage device that includes a magnetic tape recording medium used in connection with a random access recording medium, such as a hard disk drive.
In a previously proposed digital VTR system, a digitized video signal is compressed in accordance with a DCT (Discrete Cosine Transform) technique. This compressed digital video signal is recorded in oblique tracks of a magnetic tape. Each track is provided with a subcode area for storing a track number. The VTR system manages the recorded data in accordance with these track numbers. Furthermore, the capacity of such a magnetic medium to record digital data permits such a medium to record information signals in addition to the digital video signals.
Although such a magnetic tape provides a large storage capacity, when compared with other recording media, accessing the information recorded thereon is slow because a magnetic tape is essentially a sequential access medium. That is, in order to read data recorded at a predetermined position of the tape, the reading device must physically wind or unwind the tape to this predetermined position.
OBJECTS AND SUMMARY OF THE
Therefore, it is an object of the present invention to provide an information storage device in which information on a sequential access recording medium can be randomly accessed.
In accordance with this invention, an information storage device includes a sequential access store and a random access store. Information recorded in the sequential access store is loaded into the random access store. When an external device extracts selected data from the information storage device, it first transmits to the storage device a first data location marker, which is indicative of the physical location on the sequential access store that includes the selected data. On the basis of this first data location marker, the information storage device finds a previously stored second data location marker which is indicative of the location on the random access store in which is recorded the same selected data. This selected data is then read out from the random access store of the information storage medium. Thus, the present invention provides a recording medium with a large storage capacity, such as a magnetic tape, that is used in conjunction with a random access storage medium, such as a hard disk drive, resulting in effectively accessing on a random access basis, data stored on the sequential access storage medium (i.e., the magnetic tape).
Various other objects, advantages and features of the present invention will become readily apparent from the ensuing detailed description, and the novel features will be particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description, given by way of example and not intended to limit the present invention solely thereto, will best be understood in conjunction with the accompanying drawings in which:
FIG. 1 illustrates the information storage device of the present invention;
FIG. 2A illustrates the arrangement of data blocks in the hard disk drive of the information storage device;
FIG. 2B illustrates the arrangement of data blocks in the sequential magnetic medium of the information storage 5 device;
FIG. 3 is an exemplary illustration of the contents of the sector table memory of the information storage device;
FIGS. 4 and 5 are intended to be viewed together, and they 10 illustrate a flow diagram indicative of a data access operation of the present invention;
FIG. 6 illustrates a flow diagram indicative of a tape ejection process of the present invention;
FIG. 7 illustrates a flow diagram indicative of an initial15 ization of the information storage device of the present invention; and
FIG. 8 illustrates a video broadcast reception system that employs the information storage device of the present invention.
DETAILED DESCRIPTION OF THE
FIG. 1 illustrates an information storage device 2 in
2J accordance with the present invention. A hard disk drive 11 is used for recording data on one or more magnetic disks (not shown) of relatively large capacity. This recorded data is accessed randomly from the magnetic disk. A tape drive 12 is capable of driving, for example, a tape cassette of a
30 digital VTR. A different track number is assigned to and recorded in a subcode area of each track. As explained before, data recorded on this tape is adapted to be managed in accordance with these track numbers. For simplicity, data that is recorded on the digital VTR cassette shall be regarded
35 as recorded in tape drive 12.
Before proceeding to the remaining elements of FIG. 1, the discussion shall momentarily turn to FIGS. 2A and 2B, which describe the organization of data in hard disk drive 11 and tape drive 12. FIG. 2B illustrates a magnetic tape
40 comprising a plurality of oblique tracks. Each track has a storage capacity of, for example, 13.65 Kbytes, and each one of blocks bl, b2, b3, etc., comprises 1.200 of such consecutive tracks. FIG. 2A illustrates the arrangement of data recorded on hard disk drive 11. Each block Bl, B2, B3, etc.,
45 recorded in hard disk drive 11. is arranged to have a one-to-one correspondence with blocks bl. b2. b3, etc., of tape drive 12. The storage capacity of each block in hard disk drive 11 is the same as the storage capacity of each block in tape drive 12. namely. 16 Mbytes. Therefore.
50 assuming that the storage capacity of the hard disk drive is 256 Mbytes, hard disk drive 11 can store up to 16 of such blocks. Moreover, assuming that each physical sector of hard disk drive 11 comprises 4 Kbytes, then each block of hard disk drive comprises 4.096 sectors. A sector denotes the
55 minimum unit of data that is read out or written to hard disk drive 11.
As an initial matter, before any data is read from information storage device 2. the data already recorded on tape drive 12 is first loaded to hard disk drive 11. During this
60 initialization, a copy of each block of data, together with the tape location of each block, is written to hard disk drive 12.
Returning to FIG. 1, bus interface 13 is used to connect the bus of a CPU 1 or other host device or controller and the storage device 2. Data to be recorded or reproduced is
65 supplied between CPU 1 and storage device 2 through bus interface 13. When accessing storage device 2, CPU 1 designates a virtual sector number which corresponds to a