Getting back my old data after HD crash

Question

I've just erased my mac hard drive becuase it was corrupt and re-installed OSX, I did the simple erase with the disc utility.
I know the data still exists on my hard drive and will just be over written with new data when it comes along.
Is there any piece of (free) software I can use to get back my old data?
Thanks

Answer 1

Unfortunately you reinstalled OS X which means you've already overwritten the drive. You should have recovered your data before erasing the drive and reinstalling. Or better yet you should have been maintaining backups.
Basics of File Recovery
If you empty the Trash the files are gone. Recovery is possible but you must not allow any additional writes to the hard drive - shut it down. When you delete files you erase only the directory entries, not the files themselves. However, the space occupied by the files has been returned to the system as available for storage. Writing to the drive will then eventually overwrite the space once occupied by the deleted files in which case the files are lost permanently. Also if you save a file over an existing file of the same name, then the old file is overwritten and cannot be recovered.
If you stop using the drive it's possible to recover deleted files that have not been overwritten with recovery software such as Data Rescue II, File Salvage or TechTool Pro. Each of the preceding come on bootable CDs to enable usage without risk of writing more data to the hard drive.
The longer the hard drive remains in use and data are written to it, the greater the risk your deleted files will be overwritten.
Also visit The XLab FAQs and read the FAQ on Data Recovery.