TestDisk queries the BIOS or the operating system in order to find the hard disks and their characteristics (LBA size and CHS geometry). TestDisk does a quick check of your disk’s structure and compares it with your Partition Table for entry errors. If the Partition Table has entry errors, TestDisk can repair them.
However, it’s up to the user to look over the list of possible partitions found by TestDisk and to select the one(s) which were being used just before the drive failed to boot or the partition(s) were lost. In some cases, especially after initiating a detailed search for lost partitions, TestDisk may show partition data which is simply from the remnants of a partition that had been deleted and overwritten long ago.
TestDisk has features for both novices and experts. For those who know little or nothing about data recovery techniques, TestDisk can be used to collect detailed information about a non-booting drive which can then be sent to a tech for further analysis. Those more familiar with such procedures should find TestDisk a handy tool in performing onsite recovery.
[ wikipedia ]