using System.Management

string[] HdSerialNumber;

            ManagementObjectSearcher mos = new ManagementObjectSearcher("SELECT * FROM Win32_PhysicalMedia");

            int countHD = 0;

            foreach (ManagementObject mo in mos.Get())
            {
                countHD += 1;
            }

            HdSerialNumber = new string[countHD];

            int i = 0;

            foreach (ManagementObject mo in mos.Get())
            {
                if (mo["SerialNumber"].ToString() != null)
                {
                    HdSerialNumber[i] = mo["SerialNumber"].ToString();
                }
                else
                {
                    HdSerialNumber[i] = "";
                }
                i += 1;
            }