Part of Apple's keynote address at WWDC this morning was a demonstration of its new MacBook Air and MacBook Pro systems, which have not only done away with optical drives but have also streamlined other I/O offerings. In order to save space in its systems, Apple has combined USB 2.0 and 3.0 connections, but has also fallen to relying on its Thunderbolt connections to provide the I/O connectivity from older Mac systems.
As the MacBook line has evolved over the years, Apple has attempted to remove legacy ports from the systems, including the Ethernet port from MacBook Air systems, FireWire from some MacBook systems, and the ExpressCard slot from all but its 17-inch MacBook Pro.
With the inclusion of Thunderbolt in its systems, what used to be Apple's reluctance to keep a port or two has become an opportunity for it to be rid of these altogether, especially since Thunderbolt allows for the addition of any I/O technology that is needed by the user. Currently both Apple's Thunderbolt Display and upcoming third-party docking stations offer similar opportunity, though they are relatively expensive and may include features (such as a display) that are not needed.
As of the announcements in today's keynote presentation, Apple is no longer offering Ethernet, FireWire, or ExpressCard connectivity as built-in options in its laptop systems; however, the company will sell Ethernet and FireWire Thunderbolt adapters for $29 each. Currently the Ethernet adapter is available in the Apple Store, and the FireWire adapter should soon join it.
Apple's product pages state that the adapters are compatible with the latest MacBook Air and MacBook Pro with Retina Display models, without mention of any other models; however, being Thunderbolt devices they should work with any system with a Thunderbolt connection.
The loss of built-in FireWire connections means the new systems will not natively use FireWire target disk mode. While it is unlikely one could put a Thunderbolt-only system into FireWire target disk mode using the Thunderbolt-to-FireWire adapter, it should be possible to read an older FireWire system in target disk mode via Thunderbolt with such an adapter.
These adapters from Apple come with a corresponding software update that should be made available via Software Update and will be required if you use one of the adapters with your system.
UPDATE: Apple's software update for these adaptors (Thunderbolt Update 1.2) is causing some older systems to not boot. For now it may be best to avoid installing this update until the problem can be addressed by Apple.