by: MJM Data Recovery Limited
A head crash is where the read write heads come into contact with the hard drive's platters resulting with damage that causes the drive not to function correctly.
In order to understand what a head crash is, we need to know how the heads write and read data to the platters. The Heads, or Read-Write heads as they are correctly known, read and write data to the platters as magnetic flux patterns on the surface of the platters.
Modern hard drives use magnetic recording technology, which means that the magnetic surface of the platter has a magnetic pattern written to it according to the data you want to store there. As the head moves over the area where it is to be written, a small voltage is passed through the head, according to the voltage it will affect the magnetic surface directly underneat the head. This creats the magnetic flux pattern in the 'recording medium' as shown in the image below.
When data is written, the magnetic poles flip from say the N pole pointing up to the S Pole pointing up. The arrows in the diagram indicate the direction of the field.
When you place a coil that is connected to a galvanometer close to a magnet, you will see current flow in one direction or the other depending on the polarity of the magnet.
In hard drives, the polarity depends upon which pole the read head is near. Either North or South, this then is converted into binary code 0 and 1.
The physical heads float on a cushion of air a fraction of a micron (<0.001mm) above the platter surface but within the area of the magnetic field. The data is read very quickly and is converted into the word document, photo or vide that you want to load into the computer.
Please note the photos in this article were taken inside a class 100 cleanroom.
When the read write heads come into contact with the rotating platter of the drive, this is known as a head crash. The results of which can vary depending on the level of impact on the head to platter contact.
This image shows what a normal hard drive should look like. You can see that the platters have a mirror like look to them, they are much smoother than a mirror and are finely polished to get the right surface finish.
This photo shows the results of a head crash, in this instance it can be seen that much of the top platter surface has been destroyed.
In some cases where the damage is not too severe or is restricted to a single platter, it is possible to recover data from the platter areas not damaged, we have techniques for avoiding damaged areas and for physically removing heads where the damage is beyond recovery and reading from the other heads.
Obviously, there are some limits to what can be recovered using the techniques, but for smaller files like photos and word documents, etc. Some recovered data may be useful. The downside is that this type of recovery can be very expensive as it may involve several sets of heads and long periods of time whilst the cloning process is complete, and unfortunately there is no absolute guarantee of recovery.
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