AWD vs 4x4

I have a friend who is considering replacing a 2dr Jimmy with a more fuel-conscious SUV. Can someone please enlighten me, in laymans terms, what is the difference between 4x4 and AWD?
Also, along those lines, does anyone have any comments or concerns about the Chevy Equinox?
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Jerry Hamilton wrote:

You are splitting hairs, and not all AWD GM vehicles use that system. How about the open systems that use the stabilitrak to achieve traction control? The point is, whether it's 50/50 or 70/30 all four wheels are being "driven" at all times. I didn't really think that anyone would want a complete lecture on the intricasies of every GM system (there are a ton of them, as you ought to know)
Ian
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Ian,
Can you tell me what the main (mechanical) differences are between the Bravada's AWD and the "automatic 4X4" mode on my '99 Blazer (the auto button to the left of the 4WD HI/LO butons)? For some reason, I thought that the Bravada used some kind of viscous coupling, and the Blazer was entirely mechanical. I forget what it is at the moment, but I don't Chevy and Olds use the same marketing name for their auto-4X4 mode (AWD?).
Not Dead Yet
wrote:

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NotDeadYet wrote:

The Bravada AWD system uses the same basic t/case as the Blazer, but it's only a single speed. It uses the clutch pack to modulate torque to the front axle as needed. It's always engaged at a certain percentage, 5-10 percent I believe, sensors on the front and rear output shaft let the t/case module know when the front axle needs more or less torque depending on rotational differences. The clutch pack is applied as needed.
Ian
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