How can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?

Question

I have a very long string (60MB in size) in which I need to find how many pairs of \'<\' and \'>\' are in there.

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I have first tried my own way:

Answer 1

The only thing that comes to my mind is actual implementation of IndexOf iniside string class, that call

callvirt    System.String.IndexOf

which, if we use a power of reflector (as much as it possible) ends up into the

CompareInfo.IndexOf(..)

call, which instead use super fast windows native function FindNLSString: