FireWire 1394a and 1394b

The connectors

IEEE 1394a (Apple / Macintosh also "FW 400")
uses 6-pin connectors as standard, which have two lines for bus power in addition to the data lines. There are also 4-pin connectors without bus power.

IEEE 1394b (Apple / Macintosh also "FW 800")
uses 9-pin connectors as standard, FW 400 devices with 6 or 4-pin connectors can also be connected here with appropriate adapter cables.

"Bottom line: FW800 controllers are generally backwards compatible with FW400 devices."