Every single hard drive goes through a very important phase of manufacturing — precise calibration. With very dense data storage on modern HDDs, even tiny shifts during manufacturing can lead to the total failure of the device causing the electrical components to give error. This is why the process of calibration consists of numerous operations with the purpose of selecting optimal functional variables; such as correction for much precise impulse positioning and a quicker seek-time as well as adjustment of electrical currents for shifting magnetic-resistant heads, witch leads to a stronger read signal in different parts of the disk surface; the write currents are also adjusted. Values found, also known as «adaptives», are stored as tables on the disk and device operation is impossible without them. Change in spin rate of the disk will cause not only the loss of «coordinate system» for all adaptive settings (with different spin rate also changes impulse duration setting etc.) but also, for example, the height of the head hovering over disk surface, and thus, will make the read/write current settings non-functional. In other words the hard drive will not work on any speed other than on the one it is set for. Changing the manufacturer’s spin rate setting and storing them for multimode operation, on our opinion, is financially not worthwhile. We are not aware of any HDD’s that support such operational changes on the user level.
There are models that allow automatic adjustment for either 5400 or 7200 rpm during calibration depending on which is optimal but only for a single speed, not for both.
Is it possible to replace an HDD’ disk in order to fix it?
Theoretically, it is possible; moreover, it is exactly how manufacturer does it: all the HDD’s spare parts that arrive are disassembled, sorted, and new hard drives are reconstructed from these «new» components. This method actually takes a full manufacturing process with the only difference that some or components are recycled. In particular, such reconstruction cycle includes completely new variable marking on the disk. In case of replacing an identical hard disk with the data, it would be impossible to calibrate and thus, the disk will not be functioning properly.
Disk replacement is sometimes used to recover the data and this is not an easy process; as a result of such recovery the reading would be possible only once after witch the disk would be unusable.
Is it possible to recover data through constructing a “magnetization map”?
That means a creation of «magnetic map» using a magnetic field visualization technology; for example, magnetic force microscopy.
Theoretically, in our opinion, it is possible. Practically, such technology can scan fields about 100^2 micrometers in about few minutes. That means that it would take about 1 year to scan each side of a 3,5" platter,. Furthermore, those scanned fields would have to be aligned into one coherent image, magnetization transients translated into written data bits, and from this data original user files would have to be recovered.
In order to decode scanned data, it would be necessary to have complete information about coding algorithms, data positioning structures on the disk (sequence and translation algorithms) which are unique for each manufacturer, undocumented and varying from model to model.
Thus, time and equipment costs (equipment costs could rise up to hundereds thousands euros, spare parts like probes to thousands) in absolutely most cases are unacceptable for data recovery. This is not to mention other expenses required to develop a recovery technique procedure (including the research of those«confidential algorithms which are intellectual property of an HDD manufacturer).
At this time there are no devices using such data recovery, nor there are research and development of such technology.
Effort is directed to read data from an HDD using magnetic heads in a manner close to original conditions
Is it that important to use a “Clean Room” to work inside of hermetic part of the HDD?
The claim that breaking the seal of the drive outside the «Clean Room» leads to immediate permanent damage of the disk surface is strictly speaking not exactly correct. There known cases of successful procedures that where done in normal conditions. But when we talk about professional data recovery it is important to provide a reliable, high quality work. It is not acceptable for professional to take chances.
In our opinion, all claims of ability to repair without following technological standards come from people who do not have enough experience in the field and/or those who seek profit more than service quality.
From our experience, the usage of filtered workspace leads to significant increase of successful data recovery. That is of course if the hard drive did not already become an unsuccessful experiment of a surgeon who had sacrificed quality to save money.
Is it possible to recover overwritten data using the disk's residual magnetism?
There are quite often rumors that some secret labs of secret services can recover overwritten data by exploiting the effect of disk residual magnetism.
The term «residual magnetism» in this case means the trails of the previous recording, similar to the analog recording on a magnetic tape. For that case, trails of the previous record can be found on a newly created record at areas of weak signal, if erasing magnetic field has been weak.
But for the digital recording method used in HDD (the so-called «Non-return-to-zero» recording, NRZ), there are no non-magnetized areas, and magnetic level is the same at all areas. Previous erasing is not required for this method, data bits are coded by magnetization direction transitions, and every area is magnetized up to saturation to obtain maximum read signal. In contrast to an analog tape recorder, this method does not leave room for the shadows of the previous record.
Such shadows may remain only on areas that have not been re-written. For example, for stepping positioning of magnet heads, the next recording can be made with an inaccurate positioning of the head to the previously recorded track, the previous record remaining not re-written at the edges of the track. This is the case for floppy disks and, to some extent, for vintage HDDs with head stepper positioning without feedbacks. All contemporary HDDs have a solenoid actuator for their head assembly, positioning made using servo-marks built into the HDD format. Head adjustment over the track is made multiple times during a single disk turnover, that is why recording with constant shift with respect to the track center is highly unlikely in modern HDDs. There are thus no stable trails of the previous data records which presumably can be used to recover overwritten data.
Claims that there is a possibility to recover data in such way as well as there is equipment that creates «magnetization map» of an entire disk are made usually to promote data encryption/destruction equipment.