It’s an easy thing to do, you’re not quite paying full attention and you have accidentally re-formatted the wrong drive. You are going to need to perform some harddrive recovery.
The helpful answer to the question posed is:
It depends upon what exactly you did. Some of the newer Windows operating systems will zero-wipe while reformatting. If this has been done then unfortunately the data has gone. But bear in mind that to zero-wipe a drive will take some hours and if the re-format that you ran took only seconds or a few minutes then the drive has not been wiped.
What has happened is that the file table (essentially the index for the book that was your data) has been wiped. Much of your data will still be on your drive but because the operating system would look up the index to find it, it no longer knows where to locate your data.
The first and vital bit of advice is to stop using the drive that you re-formatted, every time that you access it you are potentially overwriting your missing data.
The next step is to clone the drive.
Finally run one of any number of scanning software programs on the clone, it should result in a significant amount of data.
Almost invariably you will find that at least some of the data has been overwritten by the re-format but you can get lucky (especially with some of the older Windows operating systems which don’t create such large new file table when re-formatting a drive and which therefore tend to overwrite less of the previous entries referring to your missing data).
The final problem you are going to have (and this is a very time consuming step that the cheap data recovery services tend to skip because they simply aren’t charging enough to be able to do it) is to sort through the recovered files to find out which are intact. You will find that all recovery software pulls a large number of files that are in fact corrupt when you try to open them.