Performance difference between std::unordered_map and boost::unordered_map

Hello all

we use here Visual Studio 2010 and notice quite an impressive
performance difference between the boost and std unordered_map: about
a factor 10 in favor of the boost implementation. Is there something
specified in the std which makes them slower?

boost::unordered_map 0.574148
stl::unordered_map 5.758360
stl::map 17.927353

Test code is quite simple (it uses a value of std::pair<int,
std::string>):

int g_n = 0;

void f()
{
    std::map<int, std::string> mapStl;
    std::unordered_map<int, std::string> umapStl;
    boost::unordered_map<int, std::string> umapBoost;

    const int nMaxSize = 500000;
    const int nMaxFind = 100000000;

    //create maps with 500000 elements

    //find
    {
        DBG_PRF_PROFILE_FUNCTION_TEXT("_stl_map_find");

        for (int n = 0; n < nMaxFind; ++n)
        {
            g_n += mapStl.count(n % nMaxSize);
        }
    }

   etc...
}

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