Fast text file reading in C#

This example reads a 180mb text file in 1.4 seconds on an Intel Quad Core. Here's a discussion around different methods of reading.

Note: The method listed will not reliably read binary files in (or infact unicode), as it uses a char array not a byte array.

private int _bufferSize = 16384;

private void ReadFile(string filename)
{
    StringBuilder stringBuilder = new StringBuilder();
    FileStream fileStream = new FileStream(filename, FileMode.Open, FileAccess.Read);

    using (StreamReader streamReader = new StreamReader(fileStream))
    {
    	char[] fileContents = new char[_bufferSize];
    	int charsRead = streamReader.Read(fileContents, 0, _bufferSize);

    	// Can't do much with 0 bytes
    	if (charsRead == 0)
    		throw new Exception("File is 0 bytes");

    	while (charsRead > 0)
    	{
    		stringBuilder.Append(fileContents);
    		charsRead = streamReader.Read(fileContents, 0, _bufferSize);
    	}
    }
}