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System Encryption 
TrueCrypt can on-the-fly encrypt a system partition or entire system drive, i.e. a partition or drive 
where Windows is installed and from which it boots. 
System encryption provides the highest level of security and privacy, because all files, including 
any temporary files that Windows and applications create on the system partition (typically, without 
your knowledge or consent), hibernation files, swap files, etc., are always permanently encrypted 
(even when power supply is suddenly interrupted). Windows also records large amounts of 
potentially sensitive data, such as the names and locations of files you open, applications you run, 
etc. All such log files and registry entries are always permanently encrypted as well. 
System encryption involves pre-boot authentication, which means that anyone who wants to gain 
access and use the encrypted system, read and write files stored on the system drive, etc., will 
need to enter the correct password each time before Windows boots (starts). Pre-boot 
authentication is handled by the TrueCrypt Boot Loader, which resides in the first track of the boot 
drive and on the TrueCrypt Rescue Disk (see below). 
Note that TrueCrypt can encrypt an existing unencrypted system partition/drive in-place while the 
operating system is running (while the system is being encrypted, you can use your computer as 
usual without any restrictions). Likewise, a TrueCrypt-encrypted system partition/drive can be 
decrypted in-place while the operating system is running. You can interrupt the process of 
encryption or decryption anytime, leave the partition/drive partially unencrypted, restart or shut 
down the computer, and then resume the process, which will continue from the point it was 
stopped. 
The mode of operation used for system encryption is XTS (see the section 
Modes of Operation
). 
For further technical details of system encryption, see the section 
Encryption Scheme
 in the 
chapter 
Technical Details
. 
To encrypt a system partition or entire system drive, select 
System
> 
Encrypt System 
Partition/Drive
and then follow the instructions in the wizard. To decrypt a system partition/drive, 
select 
System
> 
Permanently Decrypt System Partition/Drive
. 
Note: By default, Windows 7 and later boot from a special small partition. The partition contains 
files that are required to boot the system. Windows allows only applications that have administrator 
privileges to write to the partition (when the system is running). TrueCrypt encrypts the partition 
only if you choose to encrypt the whole system drive (as opposed to choosing to encrypt only the