While working on a presentation about iterative hashing techniques (hashing a hash n times to make it harder to break) I decided to do a few simple performance tests to see what the time tradeoff would be for more iterations. The results though confused me. When running a thousand iterations it took an average of 0.36 seconds but when I upped the iterations to 10,000 the process took less time (0.19 seconds average). I am not 100% sure why this is happening.

Here is the code I am using right now:

protected void Button1_Click(object sender, EventArgs e)
    {
        this.lblInput.Text += DoIterations(1000);
        this.lblInput.Text += DoIterations(1000);
        this.lblInput.Text += DoIterations(10000);
        this.lblInput.Text += DoIterations(10000);
        this.lblInput.Text += DoIterations(100000);
        this.lblInput.Text += DoIterations(100000);

    }

    private string DoIterations(int count)
    {
        DateTime start = DateTime.Now;

        byte[] bytes = System.Text.Encoding.ASCII.GetBytes("ThisIsMyPassword");
        for (int i = 0; i < count; i++)
        {
            bytes = ComputeHash(bytes);
        }
        TimeSpan span = DateTime.Now.Subtract(start);
        return count + " : " + span.Seconds + "." + span.Milliseconds + "<br />";
    }

    private byte[] ComputeHash(byte[] input)
    {
        SHA512Managed sha = new SHA512Managed();
        return sha.ComputeHash(input);
    }

Anyone have any ideas on why this might be happening?