DiskCryptor is a free, open source, full disk encryption software that allows you to encrypt an entire hard drive or a single partition.
It was primarily developed as a free alternative for DriveCrypt Plus Pack (a shareware program developed by a commercial company named SecurStar) and PGP Whole Disk Encryption (developed by Symantec). The encryption speed depends on your existing hardware configuration and the choosed algorithm (it supports AES, Twofish, Serpent and their combinations). You can download and use the program as a standard installer (Windows setup file) or as a WinPE plugin.
Important: Please note that after installation of DiskCryptor, a reboot is required. Also, if you intend to encrypt the system partition, it is highly recommended to create a bootable LiveCD before encryption and perform a backup volume header after encryption.
support for AES, Twofish, Serpent encryption algorithms
full encryption of external storage devices (USB drives, external HDD) including CD and DVD disks
support for AES hardware acceleration
support for SSD TRIM extension
support for various multi-boot options and compatible third party boot loaders (GRUB, LILO etc.)
support for key files and pre-boot authentication available