The safest way to Wiping Your Hard Disk Clean

Some softwares that erases files and then records over them, as the safest way to clean off a hard disk. I will suggest them follow:
If you are using a Windows PC, there are multiple programs, both free and paid, called 'file wipers,' that can do this. One I have recommended is Window Washer from Webroot, which, among other things, does what the company calls 'bleaching' of files so they can't be easily recovered. If you're using a Mac, a similar feature is built right into the latest operating system versions. It's called 'Secure Empty Trash' and is found in the Finder, the Mac's equivalent of Windows Explorer.