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The Unabridged Pentium 4 IA32 Processor Genealogy by Bob Colwell, Tom Shanley

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Memory Transaction Snooping

The Snoop's Effects on Processor Caches

When a memory transaction is snooped, the snoop result affects both the Request Agent and the Snoop Agents. There are a number of possible cases. The type of memory transaction, whether or not other caches have a copy of the line, and the state of the line(s) in other caches all have an effect. In addition, sometimes the length of the data transfer has an effect. Table 50-2 on page 1235 defines the scenarios and the results (assuming that the Request Agent is a processor).

Table 50-2. The Effects of Snoop
Transaction SnoopedSnoop ResultEffects of Snoop Result
Memory ReadMiss on all cachesThe data is supplied by memory:
  • If it is a Trace Cache line fill, the line is placed in the ...

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