Hard Disk (Very) Basics
In order to understand the differences between the EFS and the BitLocker, we have to understand some basics about our harddsisks.
First of all, we have to understand logical volumes. When you double click on the My Computer icon, you will see A:, C: and D:, given that you have a floppy drive (A:), a hard disk drive (C:) and an optical drive –CD or DVD- (D:) physically present inside your computer. Now, suppose that during the installation, you have chosen to divide your hard disk into two, let’s say you have a 250 Gigabyte capacity hard disk and you made one for 100 Gigabytes and one for 150 Gigabytes. After you complete the installation and again double click on the My Computer icon, you will see A:, C:, D: and E: drives. A is your floppy disk drive, and C: is splitted into two as C: (100 Gigabytes) and D: (150 Gigabytes), remaining E: as the optical drive. Considering that you have one physical drive, you actually created two logical volumes of 100 and 150 Gigabytes.
Then, we have filesystems and file tables. The Master File Table (MFT) is basically a database, or a list if you prefer, that keeps track of all your files on your computer. So if you move a file from one folder to another, nothing changes in your computer except the entry about the file in the MFT is changed. That is, if you move picture.jpg from My Documents to Desktop, the file actually does not move. The entry in the MFT shows Desktop instead of My Documents. What formatting the hard drive does basically is to delete the MFT and for this reason it is very possible to recover data from a formatted hard disk.
Finally we have encryption, meaning that protecting access to data except by the authenticated users.