area of the disk the height d 1 preferably ranges from about 0 1 mm to 0 6 mm and guarantees a marginal gap between the present disk and the objective lens for preventing a collision between the objective lens of an optical pickup even though the objective lens moves upward to the maximum movable distance on the condition that the present high density disk has been placed upside down alternatively other suitable height d 1 may also be used without deviating from the present invention if the disk 20 structured as above is placed normally on a spindle or turntable 11 equipped in a disk device as shown in fig7 the non protruding side of the clamping zone of the present disk 20 is in contact with the turntable 11 consequently the disk 20 is normally clamped the same as a conventional disk after successful clamping of the high density disk 20 a conventional servo controlling operation characterized by the operation of the spindle motor 12 the motor driving unit 13 and the servo controller 15 is conducted to rotate the right clamped disk 20 at a constant and high speed subsequently a focusing servo operation is conducted to focus a laser beam exactly onto a recording layer by moving the objective lens ol of the optical pickup 14 up and down within the operating distance od once the laser beam is exactly focused reproduction or recording of the high density pit patterns begins however if the present disk 20 is placed upside down on the turntable 11 as shown in fig8 the protruding side of the clamping zone of the present disk 20 is in contact with the turntable 11 consequently the surface of the disk 20 is raised.