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Magnetic Media - Tapes and Disks that store information within coatings which have the properties of Permanent Magnets. With the application of a suitable Magnetic Field by a Degausser it reverses the Magnetism in the coatings and erases the information stored on the Media.
Bulk Degausser - Is a device that can generate a Magnetic Field and apply it to all of the Magnetic Storage Media.
Degaussing - To reduce Magnetic Induction to zero by applying a reversing Magnetising Field.
Gauss - The CGS unit of Magnetic Flux Density or Magnetic Induction.
Oersteds - The CGS unit of Magnetic Field Strength - The Magnetic Field produced at the centre of a Solenoid or Coil. The Magnetic Field Strength of 1 Oersted is equivalent to Magnetic Flux Density of 1 Gauss.
Oersted Ranges - Magnetic Tape Media that is used for Data Interchange is rated by Coercivity in Oersteds or kAm. The Coercivity of Magnetic Tape ranges from 210 Oersted to 2800 Oersted. Hard disk drives do not exchange media. Therefore, hard disk drive manufacturers need not specify Coercivity. The highest Coercivity produced so far are 5000 Oersted.
Coercivity - Is a measure of the amount of Magnetic Field Intensity required to reduce Magnetic Flux Destiny in a Permanent Magnet to zero. Coercivity is often used to represent the ease with which Magnetic Media can be Degaussed, and is an average value when applied to Magnetic Storage Media. The Degaussing field strength must be much greater than average Coercivity to erase all information.
Longitudinal and Perpendicular recordings - Traditionally Hard Drives were recorded with the ‘bits’ lying flat, in a Longitudinal pattern. Over time this process became old technology as there was a requirement to record as much information in as little space as possible and in 2006 Hard Drive Manufacturers released Perpendicular recorded Hard Disk Drives where the ‘bits’ were standing up.
Degausser Strength and Destruction Capabilities - Degausser Manufacturers may specify Magnetic Field Strength in either Gauss or Oersted. In practical terms Bulk Degaussers never generate entirely uniform fields from point to point, and strength varies greatly toward point of highest possible measurement, so this specification is meaningless unless it can be assured that the specification applies to the weakest field throughout the bulk of any media to be erased.
As a general rule, a Degausser must generate strength of two to three times the Oersted rating of the Magnetic Media everywhere within its volume for significant effect. Oxide Media requires a higher ratio than Metal Media, however, Magnetic Fields and Media have “directional” properties in addition to strength. A truly effective and reliable Degaussing process must apply Effective Direction as well as Strength. When the National Security Agency (NSA) evaluate a Degausser they require the Magnetic Flux Density(G) to be three times the Magnetic Field Intensity - Oersteds. So for practical purposes a Degausser generating 10,000G can only erase 3,333 Oersteds. Therefore when purchasing a Degausser, it is critical to get both the Magnetic Flux Density - Gauss, and the Magnetic Field Intensity - Oersted measurements.