For any given disk, you can divide it into distinct partitions so that your computer sees each partition as its own disk with its own drive letter and file system. This might be useful, say, if you wanted to install one or more operating systems on the same hard drive. Because Mac OS X requires the HFS+ file system, Windows 7 requires an NTFS file system and Linux usually requires an ext2/ext3/ext4 file system, it would be impossible to have all of these operating systems on the same volume. Partitioning a single hard drive is a cost-effective and convenient alternative to purchasing multiple physical storage devices.
Partitioning is best done prior to writing any data to the hard drive. That's because re-partitioning is a notoriously unstable operation. Many disk utility and partition management programs will simply refuse to attempt to resize, split, merge, add or move partitions without wiping the entire partition table clean and starting from scratch. Other partition manager utilities claim that they can perform these tasks "non-destructively," and in some cases, they can. But whenever you begin altering an existing partition table, there's a high probability that something will go wrong.
The risk of this is that a partition table is absolutely essential to your system for reading and writing files on the disk. If the re-partitioning operation fails, the partition manager crashes, or the process otherwise is interrupted or left incomplete, it can render your entire disk unreadable. You cannot revert back to the old partition table, because in order to create a new partition table, the partition manager application will begin by completely erasing the existing table.
If this happens to you, as it has to many other users attempting to adjust their partitions without losing their data, then all hope is not lost. Your important data is still on your hard drive, but unfortunately, the file records have been altered in such a way that they cannot be found, or they appear corrupted. Imagine it as if you had hired a consultant to reorganize all of your physical files in your office and they had begun the job by pulling all the records from the shelves and filing cabinets but then walked off the job before finishing. You would have no idea what the consultant was planning on doing, nor would you know what stage of that plan the consultant was in nor why they decided to abandon the task.
It's the same with a corrupted partition table.
In these cases, your only hope is to use an advanced data recovery tool that can locate and identify files based on their signatures. File signatures are recognizable data patterns that occur in all files of a certain type. They are sort of like a fingerprint for a file, or perhaps, like a file's DNA. Most common file types have a file signature at the beginning of the file and at the end of the file. These are bits of hexadecimal code that basically say, "Begin MS Word document here" and then "End MS Word document here." By recognizing these data patterns, we can locate and recover files of a known file type, even without the partition table showing us where or how data is stored.
If we return to our consultant analogy, a file signature search would be like if you hired a different consultant and gave him the job of finding all the files and folders that contained invoices for a certain client. You would tell the consultant how to recognize your invoices and the client's name, and he would go back in and read through every single file and folder looking for these identifying clues and then bring the important information back to you out of all that mess. For a human, this would be tedious. But for a computer program, it's not.
R-Studio is a file recovery program that allows you to perform such raw file searches for hundreds of known file types. Furthermore, R-Studio supports custom known file types, meaning it can learn file signatures and find files based on data patterns that you've uncovered using R-Studio's powerful hexadecimal editor. R-Studio is highly efficient at finding and recovering files from a hard drive with a corrupted partition table. Using the raw file search, R-Studio can recover 100% of the pertinent data from a lost file. The only limitations are that it cannot recover the filename and folder path (since this information is stored elsewhere) and it cannot recover fragmented files.