Is there any good documention on how many threads are created by GCD? At WWDC, they told us it's modeled around CPU cores. However, if I call this example:

for (int i=1; i<30000; i++) {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [NSThread sleepForTimeInterval:100000];
    });
}

it opens 66 threads, even on an iPad1. (It also opens 66 threads when called on Lion natively). Why 66?

ios grand-central-dispatch
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