Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1997-04-09
2001-04-10
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S053130, C369S275300
Reexamination Certificate
active
06215748
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to data storage.
2. Description of the Prior Art
A data storage medium such as a magnetic or magneto-optical disk medium generally has “header” information to define the location, current use and properties of data files stored on the disk. The header information may typically comprise one or more lengthy tables of entries, each entry relating to a particular logical file or section of the disk.
Similar lengthy tables of entries can occur in data storage applications such as computer databases.
In many cases, the table entries are set up in the order in which the data files are recorded on the disk, or in the case of the database example, the order in which the database entries are loaded into the database. However, when a file or database entry is subsequently deleted, it is often not worth the trouble to shuffle the entire table down to fill the free space vacated by the deleted entry. Thus, after a period of usage, there will tend to be free table entries throughout the table.
Unfortunately, however, searching for such free table entries would involve sequentially reading a good deal of the table every time a new entry is to be added to the table. This data processing and storage medium access overhead is not often worthwhile, and it is easier to add a new table entry to the end of the existing entries than to try to fit it into a vacated space earlier in the table.
SUMMARY OF THE INVENTION
This invention provides data storage apparatus having an ordered data array of data items stored on a storage medium, in which deletion of a data item from the array leaves data storage space in which a newly stored data item can be stored, the apparatus comprising means for storing a mask array on the storage medium, the mask array having a respective mask array data entry for each possible data item position in the stored data array, which entry is settable to indicate whether a data item is validly stored at that data array position.
The invention addresses the problems described above by providing a relatively small “mask” array in which one or more data bits at a particular position in the mask array (preferably just one data bit) indicates whether a corresponding position in the data array is free. Thus, to locate the first free entry in the data array, only the much smaller mask array has to be accessed and examined.
This invention also provides a data storage medium on which an ordered data array of data items is stored, in which deletion of a data item from the array leaves data storage space in which a newly stored data item can be stored, the data storage medium also storing a mask array having a respective mask array data entry for each possible data item position in the stored data array, which entry is settable to indicate whether a data item is validly stored at that data array position.
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Greenwood Jonathan Mark
McGrath Mark John
Frommer William S.
Frommer Lawrence & Haug LLP.
Hindi Nabil
Smid Dennis M.
Sony Corporation
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