PGP Disk provides a software based disk encryption solution. The last freeware version was included in 6.0.2i available from http://www.pgpi.org/products/pgpdisk/ . With version 6.5, the product was dropped from the freeware offering. It is still available in later commercial versions of PGP.
According to the PGP site , “PGP Whole Disk Encryption locks down the entire contents of a laptop, desktop, external drive, or USB flash drive, including boot sectors, system, and swap files. The encryption is transparent to the user, automatically protecting data.”
I have not used one of the more recent versions of PGP Disk, but I have used older versions. While technically true that the encryption is transparent to the user, the fact that the drive is encrypted is not and may never be. The reason is simple. If you encrypt your entire drive, you are going to have to enter a key to unlock it before your operating system will boot.
The product is quite sound. I do not recall the encryption mechanism(s) used by previous versions, but the current offering utilizes only one – AES-256. That is more than sufficient to satisfy the most paranoid person’s need.
The PGP site makes reference to a single sign-on mechanism as well which makes me wonder if they truly have the encryption mechanism integrated with LDAP/Active Directory. This would not only ease the transition to their product, but is enough to make this network administrator salivate of the possibility for key escrow and recovery for dearly departed employees and their equipment. A little more research needs to be done by yours truly to see if this really is the case.