Blocking New Requests—Stop! I'm Full!

The section entitled “Transaction Tracking” on page 1147 introduced the concept of transaction tracking and the IOQ (In-Order Queue). Each agent has an IOQ that it uses to keep track of each transaction that is currently outstanding on the FSB. The depth of an agent's IOQ is device-specific. The P6 processors had a selectable queue depth of either one or eight. The Pentium® 4 processors have a selectable queue depth of one or 12. The queue depths of the various North Bridges, MCHs, or Root Complexes are design-specific. Their queue depth will be either <= the processor's queue depth.