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2012 MBP Retina — Thunderbolt Ethernet Adapter
Apple sells a Thunderbolt-to-Ethernet adapter. Mine arrived in the box with the MacBook Pro itself, as I ordered it with the MBP.
If you connect to an ethernet network, get this adapter.
It’s small, it’s convenient, it’s cheap, and it speed blows away wireless speed.
I observed sustained transfers of large files in the 85-90 MB/sec per second range (that’s ~ 700 megabits per second!), vastly faster than wireless can mange.