On hard disk, when you delete some folders, files or even an entire partition, all data is still existing in the same place where it was, and will always be there until overwritten. In fact, the deleting operation is just delete the pointer to the data on disk from MFT (Master File Table), so as to allow the operating system to perform writing operation there. Any data recovery software use this principle to work. Of course, you can delete the data truly and completely. But that requires you to ask special data eraser for help.