Hi,
This is a special feature of the 7447A called Dynamic Frequency Switching. The 7448 even has an additional DFS4 bit to divide the frequency by 4 (are there any popular systems equipped with 7448?).
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2. What about multiple cpus? Do systems with two 7447A exist? The DFS2 bit would have to be set for both. I don't know how do to it yet.
As far as the macppc world is concerned, there are 7447A and 7448 accelerators as well as dual processor 7447A and 7448 accelerators. I have macppc set up on a 7448 system if there's anything you'd like tested.
John