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.
The effect of proliferation of bad sectors will depend on what data is stored on those sectors, and may range from ‘blue-screen’ crash to clicking sounds from the drive.
This is usually a resolvable failure, though the time required for data recovery varies directly with the quantity of bad sectors present, and their location on the hard drive.
CDS uses fault-tolerant hard drive reading systems that can read the drive content dynamically in order to bypass, correct or approximate bad sector content in order to facilitate a comprehensive data recovery of data from an affected hard drive.