Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1998-08-24
2001-04-17
Kim, Matthew (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S111000
Reexamination Certificate
active
06219767
ABSTRACT:
TECHNICAL FIELD
The present invention relates to mass storage of computer systems. More particularly, the invention relates to backward skipping of logical records of one or more physical blocks of a storage medium.
BACKGROUND OF THE INVENTION
A wide variety of computer systems employ an ability to write data to and read from a remote storage medium, which can provide a number of system advantages. For example, in a distributed client/server storage environment, the ability to write data to a remote storage medium allows an application program to use hardware that is associated with processors other than the one the application program is running on.
One difficulty in accessing data from a storage medium arises from the difference between blocks which comprise a physical expression of data in the storage medium and records which are a logical expression of the data. Within a given block, there may only comprise a part of a record (herein referred to as a “segment”), an entire record or multiple records. The ability to access storage medium data by moving backward through the blocks of a tape is readily provided because blocks are the physical storage unit on the storage medium, such as a direct access storage device (DASD). If, however, an application program on a computing node coupled to the storage medium wishes to skip access records of the file rather than blocks, there is no convenient technique for accomplishing this. Again, there may be several records per block, or in the case of variable blocked spanned (VBS) format records, a logical record may be spread out over several physical blocks.
Thus, an enhanced approach to skipping through the physical blocks of a storage medium based upon logical records contained therein is desired, and in particular, a capability for skipping backwards using logical records is needed.
DISCLOSURE OF THE INVENTION
Briefly summarized, the invention comprises in one aspect a system for skipping back to a desired logical record within a physical block of a storage medium. The physical block comprises one block of a plurality of physical blocks within the storage medium. The system includes: means for evaluating a current block to determine a number of logical records within the current block; and means for determining whether the desired logical record is within the current block using the number of records int eh current block, and if so, for providing a pointer to the desired logical record for skipping back to the desired logical record.
In still another aspect, a system is provided for skipping back to a desired logical record within a physical block of a storage medium. The physical block comprises one block of a plurality if physical blocks within the storage medium. The system includes a computing unit coupled to the storage medium and having memory for holding a current block read from the storage medium. The computing unit is adapted to determine a number of logical records in the current block, and to determine whether the desired logical record is within the current block using the number of records in the current block. If the desired logical record is within the current block, then the computing unit is further adapted to provide a pointer to the desired logical record for use in skipping back to the desire logical record. Otherwise, a next previous block is retrieved from the storage medium and the computing unit's evaluating and determining processes are repeated. The retrieval of previous blocks from the storage medium continues until the desired logical record is located within a current block under analysis.
To restate, a record-based capability is provided for skipping backward through a file according to its logical record format rather than its physical format. This capability is useful since records are more likely to reflect the organization of the data than physical blocks of the storage medium. For example, if each record contains information about one client of a company, the capability of the present invention can be used to skip backwards through some number of client records. If physical blocks were used rather than records, the process of finding the client information would be more difficult. Another advantage of the capability of the present invention is that when placed into an application interface, the capability frees the calling application program from knowing the physical layout of the records. The invention will work with a number of different record formats, for example, variable, variable blocked, variable blocked spanned, fixed, and fixed blocked. Thus, an application program can call an API function which uses this invention to skip through records of a number of different formats without the application having knowledge of the formats. This frees the application to concentrate on the logical content of the data rather than its physical layout.
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Anderson Matthew D.
Gonzalez, Esq. Floyd A.
Heslin & Rothenberg, P.C.
International Business Machines - Corporation
Kim Matthew
LandOfFree
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