Bad Sectors with Degraded Head
The basic unit of data storage on a device is referred to as a ‘sector’. In most cases, a sector contains 512 bytes of information (Imagine a Notepad text file with 512 characters, equivalent to almost 4 SMS Text messages of data).
Each sector has a unique address, and this is how your system keeps track of where each file is stored. Files will usually span a number of sectors, in some cases adjacent to each other and in other cases fragmented (non-adjacent)…
Sectors store all data types, i.e. operating system files, application files, data files etc.
All hard drives contain an inherent quantity of bad (i.e. unusable) sectors when they leave the factory. The drive maintains a list of these unusable locations, and will never attempt to store data at these locations.
As time goes by during the working life of a hard drive, more sectors will become unreliable and unusable due to what are most easily described as ‘wear and tear’ effects related to the platter surface(s) in the hard drive. In this case, the read/write mechanism is properly functioning, though the actual storage medium has degraded. The hard drive also keeps track of these bad sectors.
In cases such as this one, it is deterioration of the performance of the read/write hardware components that causes data to be unreadable. Assuming the data has been written when the heads were in prime condition, the integrity of the data is usually unaffected. In this case, it is the means of reading the data (magnetically) has been affected.
This is usually a resolvable data recovery scenario, though the time required for data recovery varies directly with the quantity and position of bad sectors present and the level of degradation to the read/write heads.
In order to minimise cost, CDS will attempt data recovery without resorting to the costly approach of replacing the read/write heads. However, this does prolong the data recovery attempt, and in many cases is becomes expedient and/or necessary to replace the read/write heads in order to guarantee the best possible and fastest data recovery result.