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Apple's Thunderbolt FireWire adapter is a one-way connector

While Apple's new adapter can be attached to a computer by its FireWire connection, it will not provide Thunderbolt over FireWire.

Recently Apple made its Thunderbolt-to-FireWire adapter available, which was announced along with Apple's latest MacBook systems at this year's WWDC. This adapter offers FireWire connectivity to the latest MacBook Air and MacBook Pro with Retina Display, which do not have built-in FireWire connectivity. Since the adapter links both FireWire and Thunderbolt and can be connected to from either end, several readers have been hoping to use it as a bidirectional bridge between systems with Thunderbolt and those with FireWire.

In some cases people have wondered about the options for troubleshooting systems using Apple's Target Disk mode, where the hard drive of one can be mounted as an external drive on another system through either FireWire or Thunderbolt connections. Given that some new MacBook systems do not have FireWire, people with older systems who have purchased one of these new MacBooks might benefit from using an adapter to mount the new system's drive on the older computer.

MacFixIt reader Charles asks:

"Would [the new Thunderbolt] adapter allow a MacBook Air to connect to another computer's FireWire port in FireWire target disk mode, via the Air's Thunderbolt port?"

In addition, some people have wondered about using the adapter to allow systems with FireWire to use various Thunderbolt-based devices such as RAID arrays and even some new docking stations that are becoming available.

MacFixIt reader Keith writes:

"My current Mac Mini server came out before Thunderbolt, so it has FW800. I am now looking at adding a RAID storage unit. Can I use the Thunderbolt/FW adapter in reverse, i.e. to connect a Thunderbolt RAID array to my Mac Mini."
Apple Thunderbolt adapter
Apple's Thunderbolt FireWire adapter can connect to Macs via both ends, but can only be used in one direction. Apple

While these ideas seem reasonable and would be nice to have, unfortunately they cannot be done. The Thunderbolt adapter is a unidirectional bridge from Thunderbolt to FireWire that requires a computer host with software drivers to interface with the controller it contains. Inverting it and attempting the connection in the opposite direction will not work.

Since Thunderbolt devices have a Thunderbolt connection and controller in them, if you attach the adapter to them they will likely detect the presence of it in one way or another; however, they will have no means of using it since the RAID array does not have the appropriate drivers to interface its services with FireWire. In the case of using Target Disk mode between computers, a similar restriction is also present. The adapter will work in Target Disk Mode; however, it will only do so if first plugged into the system before invoking target disk mode so it can be initialized by the firmware.

In both situations, the FireWire protocol cannot host a Thunderbolt device, so attaching the Thunderbolt adapter to a non-Thunderbolt Mac through its FireWire connection will not provide that Mac with Thunderbolt capabilities.

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