The visual representation of emptying the Recycle Bin or Trash folders – where the data just seems to disappear – is just a convention between the operating system developer (for example Apple or Microsoft) and the end user. However, this doesn't mean that the data is gone forever, rather it's just hidden from the user and the operating system has instructed the file system to update its catalog to reflect this change. This means that the space the data takes up becomes available for overwriting but not actually overwritten, which is why data recovery is possible.
Erasing a File
Every piece of information stored on a storage medium has a well-defined place. Hard disks have platters inside, which are divided into tracks of concentric circles. These tracks are divided into sectors that have a fixed size. When you save a file on the hard drive the operating system will assign sectors to that data and the file system will remember the logical address of it, instructing the magnetic head of the hard drive to physically move to the specified sectors to read the data whenever it is needed.
When a user deletes a file, the operating system instructs the file system to mark the used sectors as available. This means that the logical address of the file is no longer valid and the index of the files is updated with this fact.
Formatting a Hard Disk
Disk formatting usually involves three different processes:
- Low-level formatting.
- High-level formatting.
Low-level formatting is mostly done by the manufacturer, but what the user can do is partitioning and high-level formatting. The latter means setting up a file system on the partition or logical volume, and each new storage medium purchased in stores comes with a file system already in place.
When you read the phrase “format the drive” or “format the volume” in how-to articles, it actually means ‘re-formatting’ or quick formatting a disk since it already contains data, which could potentially be corrupted. This process is called high-level formatting because it is performed on a working hard drive to erase all of its content. In troubleshooting articles, this suggestion usually precedes one to reinstall the operating system.
Can I Recover the Data?
The ‘problem’ with high-level formatting is that every operating system does it differently, so there is no industry standard for how operating systems erase all data found on a hard drive. Simply put, to actually erase all traces of the data, the OS needs to completely overwrite each block of data on the pre-existing storage medium, which isn't likely to happen through high-level formatting and is something that many utilities performing this process aren't capable of doing. What happens in most cases is that the OS marks the area of the disk containing information as available and retains the data until it is overwritten. If the same file system is used, though, the likelihood of overwriting the data is very small.
This leads us to the obvious conclusion that data recovery is possible even after formatting the hard drive by using data recovery software. We must note, though, that you will need to run either raw recovery or a deep scan for the software to produce the best results.
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