Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1996-06-28
2001-02-13
Vonbuhr, Maria N. (Department: 2777)
Data processing: database and file management or data structures
Database design
Data structure types
C369S272100, C711S101000
Reexamination Certificate
active
06189014
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of managing files in an interchangeable storage medium. More particularly, the invention relates to a file management method for an interchangeable storage medium having a RAM area and a ROM area, in which these areas serve as mutually independent RAM and ROM sections, respectively, and each section has a file management area for storing file management data and a file area for storing files.
In an optical disk, laser light is narrowed down to a very small beam spot having a diameter of about 1 &mgr;m to perform recording and playback of information signals. This is advantageous in that recording density is high and memory cost low on a per-bit basis. Moreover, high-speed access is possible and recording/playback can be carried out in a contactless manner. Such optical disks have been put into practical use as high-density large-capacity memories.
Optical disks can be classified broadly into optical disks (ROM disks) on which information is stored in advance and only reproduction is possible, optical disks (RAM disks) that allow information to be both recorded and reproduced, and partial-ROM disks in which a single optical disk has both of the above-mentioned features.
As shown in
FIG. 12A
, a ROM disk is such that information is recorded as pits
2
in a transparent plastic layer
1
, a metal film (e.g., aluminum)
3
is formed on the pit surface as by vapor deposition, and a protective layer
4
is provided on the metal film
3
. In a ROM disk of this kind, the signal layer (the pits and metal film) is irradiated with a laser beam LB via an objective lens OL, as illustrated in FIG.
12
B. When this done, almost all of the light returns intact from locations devoid of pits, whereas the light is refracted by pits at locations where the pits are present. Only some of the returned light actually returns to the objective lens OL since part of the light falls outside the visual field of the objective lens. Accordingly, the information can be read by using a photodiode to detect the returning light. Thus, with a ROM disk, information is recorded in the form of pits. This is advantageous in that the information is less likely to be damaged in comparison with magnetic recording, and a large quantity of information can readily be produced on a large number of disks by stamping. Such an optical disk is effective as a storage medium for electronic publishing. A shortcoming, however, is that it is not possible for the user to write information such as text on the ROM disk himself.
A RAM disk (a photomagnetic disk) is obtained by coating a disk surface with a magnetic film such as a thin film of TbFeCo. Such a disk utilizes a property according to which the retentiveness necessary for magnetic reversal of the magnetic film diminishes in conformity with a rise in temperature (retentiveness is zero at the Curie point). More specifically, recording and erasure are performed by irradiating the disk with a laser beam to raise the temperature of the disk medium to the vicinity of 200° C., thereby weakening retentiveness, applying a weak magnetic field under this condition and controlling the direction of magnetization. Accordingly, as illustrated in
FIG. 13A
, an upwardly directed magnetic field is applied by a writing coil
6
under a condition in which the direction of magnetization of a magnetic film
5
is pointed downward. When a portion at which the direction of magnetization is desired to be changed is irradiated with a laser beam LB via an objective lens OL, as shown in
FIG. 13B
, the direction of magnetization of this portion reverses, i.e., is pointed upward. This makes it possible to record information. When information is read, the magnetic film
5
is irradiated with a laser beam LB having a plane of polarization along the y axis, as illustrated in FIGS.
13
C
1
,
13
C
2
,
13
C
3
,
13
C
4
and
13
C
5
. When this is done, reflected light LBO, in which the plane of polarization has been rotated by &thgr;
k
in the clockwise direction owing to the magnetic Kerr effect, is obtained in the portion where magnetization is downwardly directed. In the portion where magnetization is upwardly directed, reflected light LB
1
, in which the plane of polarization has been rotated by &thgr;
k
in the counter-clockwise direction owing to the magnetic Kerr effect, is obtained. Accordingly, the direction of magnetization, namely information, can be read by detecting the state of polarization of reflected light. Since a RAM disk can thus be rewritten, a user is capable of writing information such as text at will, unlike the case with a ROM disk. With a RAM disk, therefore, established information such as a system program and character fonts is recorded in a prescribed area of the disk, this area is made a write-inhibit area and other areas can be used as areas for recording user-created text, additional information and version upgrading information. However, a RAM disk requires that the established information be written thermomagnetically item by item. As a consequence, fabrication takes time and raises cost.
A partial ROM (a partial-ROM photomagnetic disk) has a ROM area whose structure is identical with that of a ROM disk, and a RAM area whose structure is identical with that of a RAM disk. As a result, fixed information such as a system program and character fonts can be recorded in the ROM area by stamping, thus eliminating the need to write the information item by item. In addition, the user is capable of writing text in the RAM area at will. In other words, a partial ROM is ideal for applications in which there is a need for an area (a ROM area) that stores fixed information as well as a rewritable area (a RAM area) on one and the same disk.
FIG. 14
is a diagram for describing the construction of a typical partial ROM.
FIG. 14A
is a schematic plan view,
14
B a partially enlarged explanatory view of the partial ROM and
14
C a partial sectional view of the same. In
FIGS. 14A-14C
, the partial ROM
11
has 10,000 tracks per side, in which the tracks are concentric circles or spiral in form. All of the tracks are divided into 25 sectors (25 blocks) ST. Each sector ST is composed of 512 bytes. The header of each sector ST is provided with an address field AF, with the rest of the sector being a data field DF. Address information is recorded in the address field AF and data is stored in the data field DF. The address information includes a sector mark, a track address, a sector address and a preamble for reproducing a synchronizing signal.
The outermost band and innermost band of the storage area of the partial ROM
11
is provided with a defect management area DMA. The defect management area DMA is provided with a disk definition se ctor DDS. Media type (i.e., whether the medium is a ROM or not), RAM area information and ROM area in formation are entered in the disk definition sector DDS.
The partial-ROM photomagnetic disk
11
has the above-described physical format. The outer side of the disk is a ROM area (ROM section) ha, and the inner side is a RAM area (RAM section) lb. As shown in
FIG. 14C
, the partial ROM
11
is composed of a transparent plastic layer PLS, in which pits PT are formed in part of the ROM area by stamping, a magnetic film MGF deposited on the plastic layer PLS, and a protective layer PRF formed on the magnetic film MGF. The ROM area
11
a
and the address fields AF are formed by stamping, fixed information such as a system program and character fonts is recorded in the ROM area
11
a
in the form of the pits PT, and address information is recorded in the address fields AF in the form of pits. A track guide groove TRG (see
FIG. 14B
) used in a tracking servo also is formed by stamping. The RAM area
11
b
and the defect management areas DMA are formed by coating the entire surface of the plastic layer PLS with the photomagnetic film MGF. In this case, the magnetic film is formed on the ROM area
11
a
as well but the inner circumferential portion other than the ROM area serves as a RAM area. The rea
Nakashima Kazuo
Utsumi Kenichi
Fujitsu Limited
Greer Burns & Crain Ltd.
Vonbuhr Maria N.
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