Expansion Crystal and AGP
I'm learning about the expansion bus, and I have two questions about it that I can't figure out.
1. I've learned that the expansion bus operates at it's own set speed, 'pushed' by it's own expansion crystal. Going back a few years, when Intel came out with AGP, it sat on it's own bus connected directly to the Northbridge. Was AGP part of the 'expansion bus', and did it operate at the speed of the rest of the expansion bus, or did it operate at it's own speed?
2. I understand that the data bus and address are physically separate buses that connects the CPU and memory. As I've been reading about I/O Addresses, I don't understand if two physically separate address and data buses extend to expansion bus, or if the computer only extends one bus but somehow switches mode when communicated to expansion devices. Basically, my question is how does the CPU communicate with expansion devices along the buses?
Thanks in advance.