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The Uni-N IC includes an IEEE 1394a FireWire controller with a maximum data rate of 400 Mbits (50MB) per second. The Uni-N IC provides DMA (direct memory access) support for the FireWire interface.
The controller IC implements the FireWire link layer. A physical layer IC, called a PHY, implements the electrical signalling protocol of the FireWire interface. The PHY supports two FireWire ports by way of external connectors in the I/O bay.
The computer is capable of accepting external power through the FireWire connector to operate the PHY when the computer is turned off. While the PHY is operating, it acts as a repeater from one port to another so that the FireWire bus remains connected. For more information, see FireWire Connectors.