The Unabridged Pentium 4 IA32 Processor Genealogy

Agents Involved in the Snoop Phase

Refer to Figure 50-1 on page 1227. The following agents are involved in the Snoop Phase of the transaction:

• The Request Agent issues the transaction request. This can be one of the processors or the chipset. If the transaction is a memory transaction, the Request Agent checks the snoop result presented in the Snoop Phase.

• The Snoop Agents are the processors. They latch the transaction and, if it's a memory transaction, submit the memory address to their internal caches for a lookup. They present the snoop result to the Request Agent and to the system memory controller (located in the Root Complex, North Bridge or MCH). If the snoop resulted in a hit on a modified line in a processor's cache, that Snoop Agent ...