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Incremental computer file backup using check words

  • US 5,559,991 A
  • Filed: 06/27/1995
  • Issued: 09/24/1996
  • Est. Priority Date: 11/04/1991
  • Status: Expired due to Term
First Claim
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1. Apparatus for storing a file in an archive memory comprisingmeans for dividing said file into a plurality of blocks and for assigning respective block numbers to said blocks, each of said blocks containing a predetermined number of data bytes,means for generating for each of said blocks of said file a current check word determined as a function of the current contents of the respective block of said file and for storing each said current check word in said archive memory, andmeans for storing in said archive memory each of said current blocks of said file having a current check word different from a check word that was generated for a correspondingly numbered block of a prior version of said file stored in said archive memory, wherein different groups of stored blocks of said data bytes form respective versions of is said file, and wherein said apparatus further comprisesa global bit map comprising a plurality of bit locations corresponding to respective ones of said block numbers,means, responsive to one of said blocks being unloaded from said memory, for setting in said bit map the bit whose location corresponds with the block number of said one block, andmeans, operative prior to unloading another one of said stored blocks of a respective one of said groups, for preventing the unloading of said other one of said blocks if the corresponding bit in said bit map for said other one of said blocks had been set as a result of unloading a correspondingly numbered block of another one of said groups.

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