arch13

Firewire comes in two forms, low powered and high powered. The ipod for example, needs the high powered connection to charge while syncing. (little know fact). All onboard 1394/Firewire cards are powered via the motherboard and throttle down to unpowered as needed.
Cardbus/pcmcia cards are also powered via their bus to the laptop.
However, pci cards need to draw their power from the PS in order not to overload the pci bus on the mainboard which only runs at a max of 5 volts. If you connected, say 2 ipods to that you'd overload the pci bus with the power draw.
Cards will only draw power as needed and throttle down to unpowered as needed for connections that have a seperate power supply. For example, some firewire harddrives run of the power drawn from the connection and some have a seperate power plug.
Make sense now?

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