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Multiprocessing system including a shared cache

  • US 4,445,174 A
  • Filed: 03/31/1981
  • Issued: 04/24/1984
  • Est. Priority Date: 03/31/1981
  • Status: Expired due to Term
First Claim
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1. In a multiprocessor system, the combination comprising:

  • at least first and second processors;

    a main storage means for storing a plurality of pieces of information at main storage addressable locations;

    at least first and second private cache storage means operative with said at least first and second processors, respectively, in which a given number of pieces of information previously transferred from said main storage means are stored, including means for directly accessing said private cache storage means;

    a shared cache storage means, including means for directly accessing said shared cache storage means by each of said at least first and second processors, in which a number of pieces of information, previously transferred from at least one of said at least first and second private cache storage means, are stored;

    means for interrogating said private cache of said first processor to determine if information stored at a given main memory addressable location is stored therein, and if so, including means for accessing said information for use by said first processor; and

    if notmeans for interrogating said shared cache to determine if said information is stored therein, and if so, including means for accessing said information for use by said first processor; and

    if notmeans for interrogating said private cache of said second processor to determine if said information is stored therein, and if so, including means for determining if the information has been changed with respect to the main storage copy of the information, and if the information has been changed, including means for transferring said information to said shared cache for immediate access by said first and second processors, and if the information has not been changed, including means for fetching said information to said first processor'"'"'s private cache from said main storage means; and

    if said information is not stored in said private cache of said second processor,means for fetching said information to said private cache of said first processor from said main storage means.

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