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FW800 ports are all 9 pins. FW400 comes in two flavors, 6-pin and 4-pin (signal without power). All current MBPs still have a 6-pin FW400 port in addition to a FW800, so it's easier to just use 4 to 6-pin cable (very readily available) than adapting a FW800 cable to FW400.
 
FW800 ports are all 9 pins. FW400 comes in two flavors, 6-pin and 4-pin (signal without power). All current MBPs still have a 6-pin FW400 port in addition to a FW800, so it's easier to just use 4 to 6-pin cable (very readily available) than adapting a FW800 cable to FW400.

why cant i go to 4pin to 9pin? why is 4 to 6 better? im using a mini dv to mbp w/ 400 and 800
 
why cant i go to 4pin to 9pin? why is 4 to 6 better? im using a mini dv to mbp w/ 400 and 800

4 pin and 6 pin are both Firewire 400. 9 pin is Firewire 800, which is a different standard, although it is backwards compatible with Firewire 400, but you will get no performance improvement by doing this.

The mini DV camera or deck is only Firewire 400, and it is designed to connect to the 6 pin or 4 pin Firewire 400 connection.
 
why cant i go to 4pin to 9pin? why is 4 to 6 better? im using a mini dv to mbp w/ 400 and 800

Why would you want to? FW800 cables are generally more expensive and you'll get no performance advantage because it'll only go as fast as the slowest device on the chain (which in your case would be FW400). Save that port for something that can actually use it, like a hard drive.
 
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