File system

Details File system File system

2001-02-01

2003-12-02

Corrielus, Jean M. (Department: 2172)

Data processing: database and file management or data structures

Database design

Data structure types

C386S349000, C707S793000, C707S793000, C707S793000, C707S793000

Reexamination Certificate

active

06658439

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a file system suitable for use in recording a data sequence as a file in a recording medium such as a magnetic storage device.
2. Description of the Related Art
Random access media, such as magnetic discs and magneto-optical discs, have nowadays been taking the place of sequential access media, such as videotapes, which had ever been commonly used as a recording medium for picture data.
These random access media, compared to the sequential access media, have an advantage of giving free data accessing. In an effort to make a better use of such random access media, applications have been studied to perform various kinds of processing, such as simultaneous recording of plural pictures, time-shift replay, immediate replay from a desired position, and simultaneous processing of different types of editing.
In the random access media, a file system stores/manages a data sequence of picture information in files. There has been known a commonly used file system (hereinafter, also called “FAT file system”) utilizing a file allocation table (FAT), which file system is used chiefly in operation systems, such as MS-DOS or MS-Windows (trademarks of Microsoft Corporation) of personal computers (PC).
The FAT file system will now be described with reference to
FIGS. 2 and 16
.
FIG. 2
shows hardware of a host computer which the file system is applied to.
FIG. 16
shows a conventional FAT file system.
A host computer
1
comprises a CPU
10
, a RAM
20
, a ROM
30
, an input/output (I/O) interface
40
, and a bus
50
, being connected to a storage
60
via the I/O interface
40
.
The CPU
10
controls the RAM
20
, the ROM
30
, the I/O interface
40
, and the storage
60
. The ROM
20
and the RAM
30
are internal storages for running applications; the RAM
20
serves as a work area for the application while the ROM
30
stores such application in advance.
The I/O interface
40
inputs/outputs data to/from the storage
60
or other external devices. The CPU
10
, RAM
20
, ROM
30
, and input/output (I/O) interface
40
are interconnected via the bus
50
.
The storage
60
records various items of data in a recording medium, such as a magnetic disc and a magneto-optical disc. The description will now be made on a hard disc drive (HDD) equipped with a magnetic disc.
The CPU
10
executes an application stored in the storage
60
or the ROM
30
to function as a file system
70
′. The file system
70
′ divides the recording medium, such as an HDD, into unit record areas, or clusters, to which a data sequence is recorded, and stores/manages the data sequence as a file. The FAT is used for managing the clusters, namely, as to which cluster the data is recorded or which cluster is empty (described later in connection with the conventional art of FIG.
16
).
The file system
70
′ comprises a accessing section
71
, a cluster retrieving section
72
, a cluster allocating section
73
, and an FAT
74
.
The cluster allocating section
73
allocates a file (data) to clusters that stores currently no data (hereinafter called “unallocated”). The cluster retrieving section
72
consults with the FAT
74
(described later) to retrieve a particular cluster, namely, a file-stored (hereinafter called “allocated”) cluster or an unallocated cluster. The accessing section
71
reads out data from the allocated cluster, which has been retrieved by the cluster retrieving section
72
, and writes data to the unallocated cluster, which has been allocated by the cluster allocating section
73
.
The FAT
74
manages the clusters of the storage
60
, to which clusters a sequence of individual data of a file is allocated. Each entry of the FAT
74
stores also the number of the individual cluster that contains the next part data of the file to manage information about the connection between the allocated clusters in the form of a one-way linked list, thus managing the sequential order of those individual clusters to form the entire file. The FAT
74
manages also unallocated clusters.
With this conventional construction, for reading out data from the recording medium of the storage
60
, the cluster retrieving section
72
first consults with the FAT
74
to travel around the individual entries of the FAT
74
one after another until it meets the target cluster that stores desired data, whereupon the accessing section
71
takes access to read out such desired data.
On the other hand, for writing data into the storage
60
, the cluster allocating section
73
first activates the cluster retrieving section
72
. The cluster retrieving section
72
then consults with the FAT
74
to retrieve an unallocated cluster, whereupon the cluster allocating section
73
allocates data so that the data is written by the accessing section
71
.
However, the foregoing conventional file system would encounter the following problems:
(1) The processing, such as fast-forwarding/fast-backwarding of pictures or replaying from a desired picture frame, takes a long time because it requires random access to the recording medium.
For example, in fast-forwarding/fast-backwarding pictures, data has to be read out while jumping forward/backward over the file. Also, the replaying from the desired position requires jumping to the target cluster that stores the desired picture data.
At that time, since the FAT
74
manages information about the connection between the clusters in the form of a one-way link list, the cluster retrieving section
72
must travel around the individual entries of the FAT
74
in a sequential order until it meets the target cluster, which would take a long time to perform the processing. Specifically, if data is read out while fast-backwarding the pictures (jumping backward over the file), the cluster retrieving section
72
needs to travel around the individual entries of the FAT
74
one after another, from the head cluster of the file to a destination cluster, at every backward jumping being performed.
Accordingly, in the processing that requires random access (e.g., jump) to the recording medium, such as fast-forwarding/fast-backwarding of pictures or replaying from a desired picture frame, it would take a rather long time to retrieve a target cluster.
(2) Yet when new picture data is recorded, it still takes a long time to retrieve a cluster that stores no data (unallocated).
The FAT file system
70
′ uses the FAT
74
to manage as to whether each cluster is allocated or unallocated with data. Therefore, the cluster retrieving section
72
needs to travel around the individual entries of the FAT
74
one after another to retrieve an unallocated cluster. In particular, if only the trailing part of a single string of the clusters in the recording medium is remained empty (unallocated) the cluster retrieving section
72
needs to travel almost all the individual entries of the FAT
74
from the top until it finds an unallocated cluster, which would take a long time.
(3) Generally, in storages (e.g., HDD), of the type in which data is recorded on a disc-shaped recording medium, such as a magnetic disc or a magneto-optical disc, while the medium is rotating, and in which the Zone Constant Angular Velocity Method is employed to control rotation of the medium, the transfer rate for the inner disc region is slower than that for the outer disc region, thus resulting in a difference in transfer ability. Therefore, there is a fear that the picture data, which can be recorded in a sufficient transfer ability at the outer disc region, might not be recorded at the inner disc region.
As a measure to solve this problem, a picture data recording method is currently known in which data recording starts separately from the inner and outer disc regions toward the midst between them to realize an average transfer rate throughout the entire disc region. In the conventional file system, since the top entry and the bottom entry of the FAT
74
correspond to either the inner end position and the outer end position of the recordin

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