Mac DDR Data Recovery - Professional
Any type of data which is saved in storage device is luckily almost always recoverable. When you format a Macintosh HD, actually the files are not deleted (until they are overwritten by other files). The file system of disk is replaced with a new empty file system, thus, the entries of all the files and directories stored on the disk are erased and they become inaccessible. But hard drive maintains an index file, which tells the operating system where a particular file is stored.
When you format the hard drive, links between index and file are deleted. The file remains physically intact. You can recover files after format as long as the original files are not overwritten by others.