Does enumerateObjectsUsingBlock always always iterates sequentially?

Question

[array enumerateObjectsUsingBlock:^(NSDictionary *tool, NSUInteger idx, BOOL *stop) {
    NSLog("Idx :: %d",idx);  
}];

Will the log print indexes sequentially starting from 0 ... till end?
If YES, How is it faster than fast enumeration of kind for (obj in array)?