Why is reading bytes here so slow compared to copying the file?

Question

I'm trying to read a whole file's bytes into memory; for now, I'm doing nothing with it. Reading the file with FileInfo.OpenRead combined with a StreamReader is going very slowly; about 30 seconds as opposed to only 4 seconds to copy/paste the file from one hard drive to another in Explorer. Why would it be so slow to read it into memory? The example code:

namespace ConsoleApp1 {
    internal class Program {
        static void Main(string[] args) {
            string multiGigFile = @"path\to\my\4gb\file";
            FileInfo fi = new(multiGigFile);
            using (StreamReader sr = new(fi.OpenRead())) {
                int bufferSize = 104857600; // 100MB read buffer
                int bytesRead;
                char[] buffer = new char[bufferSize];
                // Takes ~30 secs to finish the while loop, ~4s to copy from one hard drive to another
                while ((bytesRead = sr.Read(buffer, 0, bufferSize)) > 0) {
                    Console.WriteLine($"File read; read next {bytesRead} bytes...");
                }
                Console.WriteLine($"File read; finished.");
            }
        }
    }
}

Answer 1

The StreamReader was adding a lot of overhead, converting bytes to chars presumably. Reading directly from the FileStream sped things up quite a lot.

namespace ConsoleApp1 {
    internal class Program {
        static void Main(string[] args) {
            int bufferSize = 104857600; // 100MB read buffer
            string multiGigFile = @"path\to\my\4gb\file";
            FileInfo fi = new(multiGigFile);
            using (FileStream fs = fi.OpenRead()) {
                int bytesRead;
                byte[] buffer = new byte[bufferSize];
                while ((bytesRead = fs.Read(buffer, 0, bufferSize)) > 0) {
                    Console.WriteLine($"File read; read next {bytesRead} bytes...");
                }
                Console.WriteLine($"File read; finished.");
            }
        }
    }
}