Whenever you feel like you need to recover Mac data from your internal hard drive on iMac, you want to be sure you use your iMac as little as possible because any activity could result in overwriting the data you wish to rescue. Installing Disk Drill in target disk mode or in portable mode are your best options. Be sure to have a large external drive available to save any rescued files to — preferably one large enough that you can copy your entire iMac hard drive on it. And please read this article if you have an iMac with an SSD (flash or Fusion drive).
Once you have recovered your files, be sure to turn on Disk Drill’s data protection features: Recovery Vault, Guaranteed Recovery and S.M.A.R.T. monitoring. These features will help minimize the chance of the data loss in the future and will make it very easy for you to quickly recover data on iMac hard drive.
When reading raw data from a hard drive with Deep Scan, Disk Drill doesn't care if it's FAT, NTFS, or whatever. All the data is simply a series of bits to our hard drive recovery software. This is exactly where Disk Drill starts to apply its knowledge of file signatures. And it has quite a few! Once the known signature is found, it's easy work to retrieve file types like .jpg, .doc or .xls, etc.