But like Windows Vista, if you don't have TPM, BitLocker by default will throw an error for encrypting your hard drive and will not continue. In case you are not familiar with, TPM stands for Trusted Platform Module. The benefit you get with TPM is that you don't have to store the public key anywhere else, like in a USB drive and connect it every time to access your data.

At the same time, it also ensures that no one can read the data in the disk unless it is accessed from the same machine, through the same OS and even from the same channel of the hardware connector connecting the disk with the motherboard.

if you don't have a TPM chip on your system, you can just select this checkbox in Group Policy Editor to enable BitLocker support with USB drives instead of TPM chips.

Again like Windows Vista, you can bypass the use of TPM in Windows 7 by changing some settings in the group policy and enabling the use of a USB drive instead of a TPM chip. However, the interface and options in Windows 7 Group Policy editor for enabling non-TPM encryption has changed a bit. Here is how you do it.

First open up the Group Policy Editor by typing 'Edit Group Policy' in the 'Run' window. Go to Administrative Templates>Windows Components>BitLocker Drive Encryption> Operating System Drives. Double click on 'Required additional authentication at startup', and click on 'Enable' button in the new window. This will highlight some options. Select the checkbox which says 'Allow BitLocker without a compatible TPM' and then click on 'Apply' and close the Group Policy Editor. Now you will be able to turn on BitLocker even if you don't have a TPM chip on your machine.

Running this wizard is very simple. All you have to do is to go to BitLocker Drive Encryption option in the control panel and click on the option which says 'Turn On BitLocker' just next to your drive letter. This will fire up a wizard which will either detect a TPM chip or will ask you to put in a USB drive in the machine (only if you have allowed it in the Group Policy, as discussed above) which will be further used as a key for booting up your machine. Once it captures all the details, the wizard will reboot your machine to check if it can read the USB drive while booting or not. If it passes the test it will encrypt your hard drive.