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Non-volatile memory storage and bilevel index structure for fast retrieval of modified records of a disk track

  • US 5,269,019 A
  • Filed: 04/08/1991
  • Issued: 12/07/1993
  • Est. Priority Date: 04/08/1991
  • Status: Expired due to Term
First Claim
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1. In a disk drive system which stores data in a plurality of tracks contained therein, each of said tracks containing a plurality of data records, each of said data records having an associated record number, said disk drive system having an associated volatile memory subsystem and an associated non-volatile memory subsystem, both of which subsystems are external to said disk drive system, said non-volatile memory subsystem having random-access memory for storing a plurality of said data records and a plurality of record descriptors, each of said record descriptors comprising a pointer to one of said data records in said non-volatile memory subsystem, a method for managing said data records in said non-volatile memory subsystem, comprising the steps of:

  • (a) allocating, in response to a request for writing a data record to said disk drive system, space for said record descriptors from the list of free memory locations;

    (b) writing, to said data buffer area, a copy of each said data record which has been modified in both said non-volatile memory subsystem and in said volatile memory subsystem after having been read into said volatile memory subsystem from said disk drive system;

    (c) allocating a data buffer area in said non-volatile memory subsystem for storing said data records;

    (d) tabulating, in said non-volatile memory subsystem, a list of free memory locations available for storing said record descriptors;

    (e) compiling, in said non-volatile memory subsystem, a directory of each said data record which has been modified, each entry in said directory having indicia of location of a corresponding modified said data record in said non-volatile memory subsystem;

    (f) compiling, in said non-volatile memory subsystem, a list for each of said tracks which has been read into said volatile memory subsystem from said disk drive system, each said list having entries, ordered sequentially by said record number, of the records in said non-volatile memory subsystem, each of said entries in said list having indicia of location of a corresponding said record descriptor in said directory of modified data records; and

    (g) locating said selected data record in the non-volatile memory subsystem, by indexing to the record descriptor in said list in said non-volatile memory subsystem, using the record number as an offset from the beginning of the list, to find an entry in the list, and then using the value of the found entry as an offset into said directory of modified data records to fine the entry having indicia of location of the selected data record in said non-volatile memory subsystem.

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