BitLocker To Go encrypts removable drives with AES 128-bit (or optionally AES 256-bit) encryption, so your data is protected from unauthorized users. This gives you peace of mind when traveling between Windows 7 or Windows 8 computers, but it complicates matters in earlier versions of Windows.
Windows XP and Vista can access BitLocker-encrypted drives using the BitLocker To Go Reader. However, this utility limits you to read-only access, so you won’t be able to make changes to files on the drive. Furthermore, the reader only supports FAT16, FAT32 and exFAT file systems, so if you encrypted a NTFS flash drive, you’re out of luck.
If you foresee needing complete access to the drive on earlier versions of Windows or an entirely different operating system, you will need to turn off BitLocker encryption. This potentially lengthy process reverses the previous data encryption and returns data back to its unencrypted state. This means it will be accessible on any system, but it also means it is accessible to anyone who gets access to the drive.
The time it takes to decrypt the drive depends on the amount of data on the drive and the performance of your computer. For large external drives, decryption could take several hours. However, unlike the encryption process, BitLocker doesn’t need to address unused sectors, so even large drives with few files will decrypt relatively quickly.