"The 21150 PCI Bridge is able to create another PCI bus on the card and a maximum of nine devices can be attached to this secondary PCI bus. The 21150 allows the two bridged PCI buses to operate concurrently. On the same PCI bus a master and a target can communicate while the other PCI bus is busy. In TX4 this means that the two PDC20270 controllers are linked using a secondary PCI bus and can operate while the primary PCI bus is busy. This greatly increases performance because otherwise the two controllers had to use the onboard PCI bus which could have been busy."
FULL STORY @ PCHARDWARE (http://www.pchardware.ro/Reviews/review.php?id=131)