type 
  TDiskGeometry = packed record 
    Cylinders: Int64; 
    MediaType: Integer; 
    TracksPerCylinder: DWORD; 
    SectorsPerTrack: DWORD; 
    BytesPerSector: Integer; 
  end; 
 
  TDrive = record 
    DiskGeometry: TDiskGeometry; 
    Handle: THandle; 
  end; 
 
var 
  num: Cardinal; 
  buf: array of char; 
 
procedure CloseDrive(var Drive: TDrive); 
begin 
  CloseHandle(Drive.Handle); 
  Drive.Handle := 0; 
end; 
 
function OpenDrive(C: char; out f: byte): TDrive; 
begin 
  zeromemory(@Result, SizeOf(TDrive)); 
  Result.Handle := CreateFile(PChar('\\.\' + upcase(C) + ':'), 
    GENERIC_READ or GENERIC_WRITE, FILE_SHARE_READ or FILE_SHARE_WRITE, 
    nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL or FILE_FLAG_NO_BUFFERING, 0); 
  if Result.Handle = INVALID_HANDLE_VALUE then begin 
    f := 1; 
    exit; 
  end; 
  if not DeviceIoControl(Result.handle, 458752, nil, 0, 
    @Result.DiskGeometry, SizeOf(TDiskGeometry), num, nil) 
    then begin 
    CloseDrive(Result); 
    f := 2; 
    exit; 
  end; 
  f := 0; 
end; 
 
function ReadSector(const Drive: TDrive; Sektor: integer): boolean; 
begin 
  fileseek(Drive.Handle, Drive.DiskGeometry.BytesPerSector * Sektor, 0); 
  result := ReadFile(Drive.Handle, Buf[0], Drive.DiskGeometry.BytesPerSector, 
    num, nil); 
end; 


// Beispielaufruf

procedure TForm1.Button1Click(Sender: TObject); 
var 
  Sektor: integer; 
  ok: boolean; 
  RD: TDrive; 
  P: PChar; 
  f: byte; 
begin 
  Sektor := 0; 
  RD := OpenDrive('C', f); 
  case f of 
    1: raise exception.create('Handle-Error'); 
    2: raise exception.create('Geometry-Error'); 
  end; 
  setlength(buf, RD.DiskGeometry.BytesPerSector); 
  zeromemory(@buf[0], RD.DiskGeometry.BytesPerSector); 
  ok := ReadSector(RD, Sektor); 
  CloseDrive(RD); 
  if ok then begin 
  // --- mach was, z.B.: --- 
    p := @buf[0]; 
    inc(p, 3); 
    showmessage(p); 
  // ----------------------- 
  end else showmessage('Lesen fehlgeschlagen'); 
  buf := nil; 
end;