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
06219766
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 be 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 method for skipping back to a desired logical record within a physical block of a storage medium, wherein the physical block is one block of a plurality of physical blocks of the storage medium. The method includes: evaluating a current block to determine a number of logical records within the current block; and determining whether the desired logical record is within the current block using the number of records within the current block, and if so, providing a pointer to the desired logical record for skipping back to the desired logical record.
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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