Originally Posted by gablain
If i encrypt it does it mean i have to decrypt it every time i want to access it ?
Nope once it is encrypted it stays encrypted. The encryption would appear transparent to a user. If the disk is pulled and put into another machine it can't be read without the key that is generated. If you have Windows 7 Pro or Enterprise then Bitlocker is included in it. It technically requires a TPM (trusted platform module) on your motherboard but there are workarounds for it. Easy to set up and use as it ties back into your windows user ID. (Your unlock options include no password, password, and smart card solutions)
Another option it to use TrueCrypt. It is multi-platform and been around awhile. I used it before just moving to Bitlocker. The only thing a user might notice is on older hardware the on-the-fly encryption will take a few cpu cycles. Most modern hardware in my experience doesn't have an issue with it.
Bitlocker Tutorials: http://www.howtogeek.com/howto/6229/how-to-use-bitlocker-on-drives-without-tpm/
TrueCrypt Tutorial: http://www.howtogeek.com/howto/6169/use-truecrypt-to-secure-your-data/
There are other programs and methods but those two are the best easy solutions I have come across.
EDIT: I will admit there are ways to bust the encryption but I gave it a go myself once and while possible, it is not easy.Edited by Kylepdalton - 6/13/13 at 9:40pm