Current Linux disables the device-initiated DMA mechanism for firewire and other "untrusted" busses, though it should probably consider more types of busses "untrusted" than it does. This requires the host driver to initiate DMA, which it'll only do for devices it knows how to talk to safely. Turning this protection off (and thus making the system insecure) requires both compiling a kernel with the debugging-only option CONFIG_FIREWIRE_OHCI_REMOTE_DMA turned on <i>and</i> passing a kernel parameter at boot time, so you can't do it accidentally.<p>I thought more recent versions of OS X fixed this problem as well, but perhaps not.