FileVault was introduced with Mac OS X 10.3 Panther,[1] and could only be applied to a user's home directory, not the startup volume.
The operating system uses an encrypted sparse disk image (a large single file) to present a volume for the home directory.
This encrypts the entire OS X startup volume and typically includes the home directory, abandoning the disk image approach.
For this approach to disk encryption, authorised users' information is loaded from a separate non-encrypted boot volume[4] (partition/slice type Apple_Boot).
The original version of FileVault was added in Mac OS X Panther to encrypt a user's home directory.
Without Mac OS X Server, Time Machine will back up a FileVault home directory only while the user is logged out.
Using Mac OS X Server as a Time Machine destination, backups of FileVault home directories occur while users are logged in.
[8] A free space wipe using Disk Utility left a large portion of previously deleted file remnants intact.
[3] The I/O performance penalty for using FileVault 2 was found to be in the order of around 3% when using CPUs with the AES instruction set, such as the Intel Core i, and OS X 10.10.3 Yosemite.