You slightly misunderstood jennifer post. That was referring to if you plug a 10g end device into a 1g port on say a switch. That connection between that device and the switch will negotitate to 1g.
The confusion comes in part because the data can pass between actual end devices can pass a different speeds. You only think there is a direct connection between the 2 end device. The switch is in the middle making things work.
Lets say you have 1 pc connected to the switch at 10g and a second device connected at 1g. The traffic will pass between the first pc and the switch at 10g. The buffer will be moved to the port going to the 1g device and sent at 1gbit. This works fine as long as the 10g device does not try to send...