The Microsoft Store has two version of Windows 8: Windows 8 Pro, and Windows 8 Pro Pack:
What is the difference between these versions of Windows 8?
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Windows 8 Pro allows you to upgrade from an older version of Windows (XP, Vista, 7) to Windows 8 Pro.
Windows 8 Pro Pack allows you to upgrade from a lesser version of Windows 8 to Windows 8 Pro.
The Windows 8 Pro Pack is just license to move a Windows 8 installation to Windows 8 Pro with Media Center. It does not contain any physical media.
The Windows 8 Pro Pack enables you to move up to Windows 8 Pro. Your PC or tablet must be running Windows 8 to use Windows 8 Pro Pack. The Pro Pack makes your PC or tablet ready for business by adding professional-grade features by adding:
Encrypt your data with BitLocker: BitLocker drive encryption helps protect corporate data on mobile PCs that include a TPM chip. BitLocker now encrypts hard drives more quickly, helping to keep your data safe without interrupting your productivity. BitLocker now supports encrypted drives, too.
Stay safer with SmartScreen: SmartScreen services help protect you from malicious sites and software on the Internet. It checks the reputation of any new app or website, helping to keep you safe no matter what browser you're using. That helps prevent malware and other viruses from infiltrating your PC, or your corporate network.
Connect to company networks with DirectAccess: Just because you're not in the office doesn't mean you're not working. DirectAccess allows remote users to more securely and seamlessly access resources inside of a corporate network without having to launch a separate virtual private network (VPN) connection.
Windows Media Center: Windows Media Center lets you turn your PC into a home entertainment system that can play and record high-definition TV (if you have additional tuner hardware), DVDs, and CDs. It's also a software DVR that can play photo slideshows and Internet TV content.