Disk encryption software is an added line of defense in thwarting bad guys from entering your computer. The most popular disk encrypting software I've used and many other was TrueCrypt,sadly the developers of such software stop adding updates and it is now discontinued,in comes the next best thing VeraCrypt.
Like TrueCrypt, VeraCrypt is an open source free utility software that uses on-fly encryption. Users can create a virtual encrypted disk either within a file or you can encrypt an entire partition. You can even encrypt an entire storage drive or device with pre-boot authentication,meaning as soon as your computer boots up, you'll need to type in a password to access files within that storage device. Forgetting that password will render you computer useless, you'll end up having to erase data and reinstall your entire operating system so its important that you backup all of your content before using VeraCrypt.
VeraCrypt is based on several algorithmic encryption that includes AES,Serpent, and Twofish. Addtionally, it has five different combinations of cascaded algorithms that is available: AES-Twofish, AES-Twofish-Serpent, Serpant-AES, Serpent-TwoFish-AES and TwoFish Serpent.
Now there is a downside to using VeraCrypt, as of late the software is susceptible to malware and virus attacks, so it is important that users constantly add updates to the software. Secondly, the software has a very steep learning curve,so carefully follow its step-by-step directions.
Other than the mentioned downside, VeraCrypt is definitely the software you should add to your line of defense. Remember,make sure your aware of updates that's being posted by VeraCrypt and carefully read its instructions.