The data recoverability or the overall security of the hard drive destruction process is a factor that has become more and more important as the number of obsolete or replaced hard drives has grown. What is sufficient to ensure that the data contained on a hard drive is unrecoverable?
It is useful to consider the mechanics of the way hard drive data is placed on the drive. Each individual manufacturer of hard drives has their own process that controls the read mechanism and electronics of how data is actually written to the platters in the hard drive. There is no defined standard that is used and each company utilizes the encoding that it deems optimal. Furthermore, each model of the hard drive and even the firmware used on that model would have to be known in order to recover information. This is contrary to the situation with a CD/DVD. The data recorded is always recorded in the same manner. Therefore, if you have a CD/DVD it can be read with the standard reader contained in every computer. Contrast this with the hard drive. Each hard drive is self contained. It has the reader and firmware in the drive which is then used to recover the information that is written on the disks.
By shredding a hard drive and mixing the shred with other hard drive materials, the process of recovering data become virtually impossible. A fragment of a drive would need to be recovered and then a process utilizing magnetic force microscopy (MFM) would have to be employed. This is the only process that does not require the platters of the hard drive to spin and the heads to read the data. The MFM allows the data to be viewed in an encoded format. However, the logistics are staggering. The MFM takes a picture of each bit on the disk. Each picture will be 100 bytes in size. For a 20 Gig drive approximately 160 billion bits would need to be photographed. Secondly, each photograph would need to be analyzed by an expert to interpret each bit. Any error in reading or interpretation would produce meaningless data results.
In order to reduce the chance of recover-ability of data, a hard drive should be separated from the casing which contains the firmware and model information. Alternately, the platters can be destroyed through a degaussing process whereby a strong magnetic field of sufficient force is directed on the hard drive. Unfortunately, after degaussing, the drive appearance will remain the same and the hard drive would have to be tested in order to ensure the destruction of the data on the platter. Physical destruction through shredding of a hard drive is the clearest means of visually ensuring that the data contained on the platters is unrecoverable on a practical basis. The platters are physically destroyed and separated from the information bearing cases in which they were housed. The resulting shredded materials make it virtually impossible to recover any data that is contained on them and the security of the information will be ensured.