Its been discovered by Anandtech that the new 2011 MacBook Air
recently launched by Apple is fitted with a weaker Thunderbolt chip than
other Apple systems such as the iMac, Mac Mini and MacBook Pro.
All systems apart from the MacBook Air use a full sized Thunberbolt
controller chip called the Light Ridge, but Anandtech have discovered
the new 2011 MacBook Air is equipped with a less powerful and scaled
down version of the chip called the Eagle Ridge.
The weaker Thunderbolt chip has probably
been included by Apple in the slim MacBook Air to save space and power
and shouldn’t cause too many problems to users, unless you are looking
to daisy chaining two monitors. As the Eagle Ridge will not support more
than one external monitor, or you need to push larger amounts of data
as the weaker chip will only support transfer speeds slower than the
full Thunderbolt chip that is capable of data speeds of up to 10 Gbps of
Source: Apple Insider : Anandtech : Image iFixit