heres another one of my dumb questions

, what is the difference between the regular transfer case and the auto transfer case? Is it all wheel drive when u hit the auto 4wd button? im a little confused

i ask because im thinking about getting a newer blazer/jimmy, silverado/sierra, or tahoe/yukon. most of the pickups or tahoes/yukons that are 4x4 have this button and i just wanted to know more about it.
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2000 Chevy Blazer ZR2
Performance Mods: Numerous
Suspension Mods: Some, but not enough
Exterior Mods: Just Right
1987 Buick Turbo T Dark Red
Low 11 sec sleeper

.030 4.1 block, PT6262E, & other odds and ends....
My Cardomain