METHODS AND DEVICES FOR RECORDING OR READING FILES ON/FROM A SEQUENTIAL MEDIUM AND SEQUENTIAL MEDIUM
 The invention relates to the recording and reading of files on a sequential medium including recording or reading of a management information area storing data structures that are used for volume and file management and recording or reading files onto the volume. Furthermore, the invention relates to a sequential medium comprising such a management information area and a volume containing files.
 Known optical digital video recording discs consist of a lead-in, a data and a lead-out area. A drive presents the data area to the file system. In general, a file system uses part of the data area for its own administration purposes and presents the remainder in some suitable way, using partitions, as a so-called logical volume, i.e., a logical contiguous address space to an application. Typically a file system uses an anchor descriptor at so-called anchor points to find a reference to its management information area for volume structure.
 JAFS (Joint Approach File System) is a volume and file management system intended to be used for both AV (Audio and Video) and computer applications. Most of the existing volume and file management systems are designed to be used only for computer applications, therefore they lack the functions necessary for AV applications such as real time data reading and writing, or file dividing and combining without data movement. JAFS is designed to enable implementation of the above and other functions usefull for AV applications in an effective manner.
 The JAFS file system is defined for a randomly rewritable medium. Due to this definition problems occur, when using a sequential write-once medium.
 It is therefore an object of the present invention to provide a definition of such a file system that also works for a sequential write-once medium.
 This object is achieved by providing a method for recording files as set forth in claim 1, a method for reading files as set forth in claim 7, a device for recording files as set forth in claim 8, a device for reading files as set forth in claim 9, and a sequential medium as set forth in claim 10.
 The invention enables to modify, in particular add or remove, files on a sequential, in particular write-once, medium such as a DVR-R (digital video recorder-recordable) medium. Thereby, the management information area needs to be updated by writing a new version of the management information area. As the data already recorded on the medium cannot be rewritten in a sequential writeonce medium the management information area has to be written as a new version at the end of files or data, such as management information area data already recorded on the medium.
 Thus, new files added to the existing files are being registered in a new version of the management information area. Accordingly, removed files are no longer registered in the current management information area, thus appearing to be deleted, even though the data of these removed files is still on the medium.
 As the management information area according to the present invention is located at the end of the files
recorded on the medium, it is a problem to quickly find the current version of the management information area. However, a file system descriptor being located somewhere after the lead-in, i.e. at the beginning of the data track between the lead-in and lead-out area, points to the management information area. Thus, the management information area can be accessed rapidly.
 The file system descriptor is written in a reserved track that is located somewhere after the region of a lead-in area, i.e. near by the beginning of the medium. Thus, the file system descriptor maybe accessed instantaneously. As the file system descriptor is written in a reserved track having a capacity, in particular in terms of bytes, being much larger than the file system descriptor itself, new file system descriptors may be written in the reserved track in order to specify the current location of the management information area.
 Embodiments and modifications may be taken from the sub-claims and will be described in more detail with reference to the accompanying drawings, in which:
 FIG. 1 shows a diagram of a data system of an optical DVR disc according to the prior art JAFS specification;
 FIG. 2 shows a data system according to a preferred embodiment of the present invention;
 FIG. 3 shows an anchor descriptor;
 FIG. 4 shows a schematical diagram of an device for recording and/or reading files on an optical DVR disc.
 The following definitions are used in connection with the present invention:
 The term "medium"0 defines means on which data is recorded.
 The term "management information area" or MIA is a set of physical or logical sectors of which the sector numbers are consecutive. It is used to record data structures in units of physical or logical sectors. Data structures that are used for volume and file management are stored in the management information area. Various pieces of information about a volume are recorded in a management information area.
 Preferably, in order to assure reliability, two management information areas for volume structure, in which two identical sets of information are recorded, shall be recorded on a physical volume. These are referred to as the main management information area for volume structure and the reserve management information area for volume structure.
 The term "partition" represents a collection of physical sectors with continuous physical sector numbers in a physical volume.
 The term "logical volume" is defined as a sequence of partitions. A logical volume may have partitions on different physical volumes. Thus, a logical volume may be constructed from partitions belonging to different physical volumes.
 The term "descriptor" specifies the starting address and size of the main anchor or the reserve management information area and the location of the management information area map in the main and the reserve management