The Unabridged Pentium 4 IA32 Processor Genealogy

The FSB Interface Unit

The Agent Types

There are three types of agents involved in a FSB transaction:

• The Request Agent issues the transaction request.

• The Response Agent is the device that acts as the target of the transaction.

• The Snoop Agents are the entities that contain caches (typically, the processors). If the transaction is a memory transaction, they perform a lookup in their caches using the transaction's address and report the snoop result (to the Request and Response Agents) in the transaction's Snoop Phase.

The Request Agent Types

There are two types of Request Agents:

• The Symmetric Request Agents are the processors. They use a symmetric (rotational) bus arbitration scheme.

• The Priority Agents are agents other than processors that perform ...