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Computer disk with security protection

  • US 4,967,184 A
  • Filed: 09/19/1989
  • Issued: 10/30/1990
  • Est. Priority Date: 09/19/1989
  • Status: Expired due to Term
First Claim
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1. An improvement in security protection of computer disks of the type having a central aperture, a drive hub located in the aperture, the hub having a circumferential flange overlying the perimeter of the substrate aperture and at least a portion of the hub comprised of a ferromagnetic metal adapted to cooperate with a magnetic disk clamp in a disk drive apparatus, means for securing the disk substrate to the hub flange and a ring-shaped surveillance marker formed around at least a substantial portion of the aperture periphery between the disk substrate and the hub flange, the improvement comprising:

  • said ferromagnetic hub metal having a coercivity greater than the coercivity of the surveillance marker and less than the field intensity of the magnetic field employed in the detection zone of a surveillance portal to detect the presence of the surveillance marker as the disk is carried through the portal.

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