C# What is the performance relationship with the storage device in the memory mapped file?

Place the R drive (RamDisk using Imdisk) and the C drive (SSD) in the memory mapping file, respectively.

However, there is a large difference in disk read and write speed, but there is little difference in memorymappedfile performance.

Why is the performance of a memory mappedfile not proportional to the performance of the disk?

this code used performance test C and R driver. args[0] is file path in C or R driver.

The stopwatch count is the same no matter which drive is selected.

using System.IO;
using System.IO.MemoryMappedFiles;
using System.Runtime.InteropServices;
using System.Diagnostics;

class Program
{
    static void Main(string[] args)
    {
        int i = Int32.Parse("100");
        Console.Write("count " + i + ", ");
        string path = "C:\\Users\\TBB_miniPC\\Desktop\\dummy\\ain.jpg";
        FileStream file = new FileStream(path, FileMode.Open);
        BinaryReader reader = new BinaryReader(file);

        byte[] buffer = new byte[file.Length];

        reader.Read(buffer, 0, buffer.Length);
        reader.Close();
        file.Close();

        long offset = 0x00000000; // 0 megabytes
        long length = 0x10000000; // 256 megabytes
    
        Stopwatch sw = new Stopwatch();


        sw.Start();
        using (var mmf = MemoryMappedFile.CreateFromFile(args[0], FileMode.Open, "die", buffer.Length+1) )
        {
            using (var accessor = mmf.CreateViewAccessor(0, buffer.Length))
            {
                while(i > 0)
                {
                    accessor.WriteArray<byte>(0, buffer, 0, buffer.Length);
                    i -= 1;
                }
                sw.Stop();

                Console.WriteLine("time" + sw.ElapsedMilliseconds);
            }
        }
    }
}