If you are concerned about protecting the data on your hard drive, you probably have a password set on your Operating System, such as the Windows login password, and you may be using NTFS which allows you to set permissions on your files and folders. You may even be using some third-party encryption software that enables you to encrypt the entire contents of your hard drive, or perhaps you're using the encryption features that come standard with recent versions of Microsoft Windows. If you've gone to the trouble of deploying these security features, you should also consider features provided by the BIOS provided by most manufacturers.
BIOS, the Basic Input/Output System is the "firmware" that's built into your computer's motherboard that boots up the PC and loads the operating system. The first screen you see when you turn the computer on is typically a splash screen for the BIOS. It often has a message instructing you to press a particular key to enter the setup for the computer, which is really just configuring BIOS options. This is where you configure power-saving settings, and a bunch of other details most users could care less about.
However, there will likely be a few security settings as well. Most common is a simple password that prevents anyone from booting the PC w/o entering the password. That's great, but it's pretty simple for a thief to get your data by popping the case open and moving your hard drive to another PC. This bypasses the "power on" password because it's stored in the BIOS, not in your hard drive.
To solve this problem, most BIOS makers also have a "hard drive password" actually stored on the hard drive. If a thief puts this hard drive in another PC, he will still get a password prompt before he can access the data.
One last thing to check is a case-alarm feature. This is typically a wire that connects to your desktop's case. If someone opens your computer's case it breaks the circuit, and you'll get a message the next time you log in, which lets you know someone was tampering with your computer.
Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.