Which one is faster data types in .NET or data types in C#?

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C#

.NET

Hi to all first of all i am sorry because my first language is not english I want understand which one is faster C# data types or .net data types i try to understand by below code and i think .net data types is faster(is this correct?) i test this code both with x86 and x64 platform.

StopWatch SW=new StopWatch();
SW.Start();
for (Int32 i = 0; i < 99999; i++)
{
    for (Int32 j = 0; j < 999; j++)
    {
        Int32 a = 37;
        Int32 b = 37;
        Double c = Math.Pow(a, b);
        String d = "abcde";
        String e = "abcde";
        String f = d + e;
    }
}
Console.WriteLine(SW.Elapsed.TotalMilliseconds);
SW.Stop();
Console.ReadKey();

and second code

Stopwatch SW = new Stopwatch();
SW.Start();
for (int i = 0; i < 99999; i++)
{
    for (int j = 0; j < 999; j++)
    {
        int a = 37;
        int b = 37;
        double c = Math.Pow(a, b);
        string d = "abcde";
        string e = "abcde";
        string f = d + e;
    }
}
Console.WriteLine(SW.Elapsed.TotalMilliseconds);
SW.Stop();
Console.ReadKey();

in this link Difference Between Data Type in C# and Data Type in .NET[^] "said all data types are converted into .Net Data type"What does this mean?I think if this word is true so converting C# alias data types to .net data types it takes time and i tested this by above codes but i am not sure if anyone sure(not unsure) please answer me thanks a lot

What I have tried:

i trying in console and winform with visual studio and without it