Everything you need to know about the HyperTransport bus used by AMD processors, including the most common mistakes people say about it. You can read it at HardwareSecrets.
Here is a snippet:
"Current AMD processors have two external busses. One is used on the communication between the CPU and the memory, and it is simply called "memory bus." The other is used on the communication between the CPU and all other PC components through the motherboard chipset and is called HyperTransport - an I/O (Input/Output) bus. In this tutorial, we will be explaining how the HyperTransport bus works and clarifying common mistakes people assume about this bus."