Rehber Buffer nedir ve nasıl kullanılır?

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e){

    string file_path = e.Argument.ToString();

    byte[] buffer;
    int bytes_read;
    long size;
    long total_bytes_read = 0;

    using (Stream file = File.OpenRead(file_path)){

        size = file.Length;

        using (HashAlgorithm hasher = SHA256.Create()){
            do{
                buffer = new byte[8192]; // 8KB aralıklarla belleğe toplu olarak yazacak

                bytes_read = file.Read(buffer, 0, buffer.Length);
                total_bytes_read += bytes_read;
                hasher.TransformBlock(buffer, 0, bytes_read, null, 0);
                backgroundWorker1.ReportProgress((int)((double)total_bytes_read / size * 100));

            }while (bytes_read != 0);

                hasher.TransformFinalBlock(buffer, 0, 0);
                e.Result = HashStringRotate(hasher.Hash);
        }
    }
}

private static string HashStringRotate(byte[] hash_bytes){
    StringBuilder hash = new StringBuilder(32);
    foreach (byte be in hash_bytes){
        hash.Append(be.ToString("X2").ToUpper());
    }
    return hash.ToString();
}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e){
    progressBar1.Value = e.ProgressPercentage;
    ProgressPercentLabel.Text = "%" + e.ProgressPercentage;
}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e){
    HashLastLabel.Text = e.Result.ToString();
}

private void FileSelectBtn_Click(object sender, EventArgs e){
    OpenFileDialog ofd = new OpenFileDialog{
        InitialDirectory = @"C:\Users" + Environment.UserName + @"\Desktop\",
        Title = "Dosya seçiniz",
        Filter = "Tüm Dosyalar (*.*)|*.*",
     };

     if (ofd.ShowDialog() == DialogResult.OK){
         FileSelectTextBox.Text = ofd.FileName;
     }
}

private void StartHashBtn_Click(object sender, EventArgs e){
    if (FileSelectTextBox.Text != ""){
        backgroundWorker1.RunWorkerAsync(FileSelectTextBox.Text.Trim());
    }
}