R>class Program
R>{
R>    static async Task Main(string[] args)
R>    {
R>        const int FILE_FLAG_NO_BUFFERING = 0x20000000;
R>        const int BufferSize = 256 * 1024;
R>        const string Path = @"c:\iso\myiso.iso";
R>        const int TaskNumber = 16;
R>        const byte Pattern = 42;

R>        var totalLength = new FileInfo(Path).Length;
R>        var timer = Stopwatch.StartNew();
R>        var tasks = new Task<int>[TaskNumber];
R>        for (int i = 0; i < TaskNumber; i++)
R>        {
R>            var options = (FileOptions) FILE_FLAG_NO_BUFFERING | FileOptions.SequentialScan;
R>            var fs = new FileStream(Path, FileMode.Open, FileAccess.Read, FileShare.Read, BufferSize, options);
R>            var position = i * BufferSize;
R>            tasks[i] = Task.Run(() => Worker(fs, position, TaskNumber * BufferSize, BufferSize, Pattern));
R>        }
R>        var result = await Task.WhenAll(tasks);
R>        var speed = totalLength * 1000 / timer.ElapsedMilliseconds / 1_000_000;
R>        Console.WriteLine($"Read {totalLength} bytes for {timer.ElapsedMilliseconds / 1000.0} seconds. Speed is {speed} Mb/s");
R>        Console.WriteLine($"Found {result.Sum()} occurences of byte {Pattern}");
R>    }

R>    private static int Worker(FileStream fs, long position, int step, int size, byte pattern)
R>    {
R>        var totalLength = fs.Length;
R>        var result = 0;
R>        var buffer = new byte[Math.Min(1024, size)];
R>        while (position < totalLength)
R>        {
R>            fs.Seek(position, SeekOrigin.Begin);
R>            var count = (int) Math.Min(size, totalLength - position);
R>            while (count > 0)
R>            {
R>                var read = fs.Read(buffer, 0, buffer.Length);
R>                for (int i = 0; i < read; i++)
R>                {
R>                    if (buffer[i] == pattern)
R>                    {
R>                        result++;
R>                    }
R>                }
R>                count -= read;
R>            }
R>            position += step;
R>        }
R>        return result;
R>    }
R>}
R>