Yup
AVCHD is highly compressed. You've got to trade storage size for the ability to do real-time editing. (Assuming your system has the horsepower to deal with the bandwidth in the first place.) That G/min is what you have to inflate it to before you can work with it.
There are a few apps now that can work with the raw AVCHD files in real time, but you're looking at 8-core Mac Pro with 4G.
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Drew