How to format hard disk so that no data is recoverable?
No matter if you have deleted files from recycle bin, it can be recovered. It would remain at its place until being overwritten. That is exactly how you would be able to recover the file that has been deleted. But, there are occasions when you would not want the deleted files to be recovered. How would you be able to do it? Let us check it out.
Even when you format a hard drive, no data on it is deleted. The Windows operating system is informed that the space occupied by this data is available for overwriting. In fact, the operating does not "see" it and thus the drive appears blank. That is precisely what we are interested in. How to completely erase a hard disk so that it cannot be recovered. There are several ways to wipe a drive completely. We will discuss a few ways that this task can be achieved.How to format a Hard Disk permanently?
There are multiple ways that can be used to wipe hard drive completely. However, the method you would adopt should depend upon the purpose of the data deletion. If you are looking to reuse the hard drive after formatting it, it would be advisable to use a Data Destruction Software.
Let us check out the best software tools that would help you wipe your data completely.HardWipe
The software offers you multiple functionalities. You can choose from several options like wiping recycle bin, erasing the free space, wiping a drive or volume or even shredding your files or folders. 
The free version comes with ads, but you can opt for the Pro version if you feel annoyed with them. What makes the tool an exciting option is the ability to choose between multiple wiping algorithms. You can choose to wipe the data using multiple passes right from one pass to 35 passes. You can also rename the file 10 times so that you would be able to minimize the chances of filename recovery.
A few other options available with the tool include a speed mode that would improve the speed of operation and an Auto Power off option so that the system can switched off automatically after the wiping operation is completed.
For more details, visit the official site at http://www.hardwipe.com. It comes with an installer version and a portable version. File Shredder
Unlike HardWipe, Fie Shredder does not offer you a portable version. It would work more as a permanent application in the form of an installer version. 
It is one of the excellent tools and lets you wipe your data completely. This can be the most reliable, faster and safer option to delete your files and drives. What makes it an interesting option is the fact that it is available for free. In fact, an excellent utility par excellence is what would make it a great option in its own right.
File Shredder offers you five different wiping algorithms that you can choose. Some of the algorithms would include 1 or 2 pass, DoD level 3 pass, and Secure 7 pass. You also have access to Disk Wiper functionality that should help you wipe unused disk space. You can also use the tool to erase certain specific folders and drives on your hard drive.
You can download it for free at http://www.fileshredder.org/index.php. Cyber Shredder
Cyber Shredder is what would help you wipe the data with ease. In fact, the smaller and compact footprint should be what would make it an excellent service. It is a quicker, safer and excellent tool for your needs. 
You would definitely love the simple interface that the tool offers you. Cyber Shredder lets you wipe your hard drive using any of the three powerful algorithms. You may use a Very Quick Pass option that performs a single pass, a Quick Pass that would work with three passes and a Normal Pass option which is indeed a NSA approved 7 pass algorithm. The tool also renames the files multiple times as a means of doing away any chance of file recovery through file name recognition. The tool offers you a portable version that should be ideal for quicker data wipe functionality.
Want to give it a try? Check it out at https://www.cylog.org/utilities/cybershredder.jsp.Destroy the Hard Drive
Well, this is the method that can be helpful if you do not want to reuse the hard drive but want to discard it. But, discarding it by throwing it out may not be a good idea for obvious reasons.
Even when you have deleted all the files and other data from your hard drive before removing it, you have already left a chance of your privacy being breached with the data being left out in the open.
Whether you want to throw out in the open or not, make sure you have destroyed it completely. Even when your hard drive is damaged and cannot be used, data recovery tools can be employed to extract data from these drives. If you do not want your privacy to be violated, destroying your non-working hard drive is the best option you can go through.The Concluding Thoughts
Wiping your hard drive completely is the right option if you want to dispose of your hard drive or want to sell it off to somebody. Mere deletion of the hard drive data may not be the right option in either of those cases. Ensure that you have completely erased the files and other data on your drive so that you can rule out the possibility of your data being recovered.
If you do not wipe the data, you would be running the risk of violating your sensitive data. You can use any of the above methods and tools for erasing the data on your hard drive. If your hard drive is not working anymore, you can destroy the drive so that you would never be able to recover any data from it.
Wiping data using random 0's & 1's can be permanent & secure way of formatting a data, such that no data is recoverable. I recently added the NAID Conferance and get to know about another interesting software ( named BitRaser) which was not mentioned above. Other than that for folks who are looking for free, DBAN is all time favourite.
I suggest to wipe using US DOD (3 pass/7 pass) or NIST standards algorithm.