function GetDiskSerialNumber(value:char):string;
var
  VolumeLabel, FileSystem: Array[0..$FF] of Char;
  SerialNumber, DW, SysFlags: DWord;
begin
  result:='';
  Value := UpCase(Value);
  if (Value >= 'A') and (Value <= 'Z') then
   begin
    GetVolumeInformation(PChar(Value   ':\'), VolumeLabel, SizeOf(VolumeLabel),
                         @SerialNumber, DW, SysFlags,
                         FileSystem, SizeOf(FileSystem));
    result:=format('%x',[SerialNumber]);
   end
end;    procedure TForm1.Button1Click(Sender: TObject);
begin
  caption:=GetDiskSerialNumber('C');
end;