Using your copy of Windows on more than one Computer?

My neighbor, Ernie, has a family of six, and he added a third computer to his home last week. The two computers he already owns use the Windows XP operating system. The computer he just bought came with Windows Vista installed. After Ernie tried Vista for a few days, and after talking with a few friends, he decided that he wanted to remove Vista from his old computer and replace it with the older Windows XP that his family was accustomed to using.

Ernie's question to me was this: “Can I remove the pre-installed Vista from my new computer and replace it with a copy of Windows XP that I already own?”

Generally, the answer is, “not unless you uninstall Windows XP from the other computer, first.” The Microsoft Licensing agreement for most Microsoft is for one computer at a time, unless you have a corporate or site license. The technical issues may be a bigger problem than the legal one.

When you first install the Windows Operating system, it will ask you for the 20 character product code. The last five characters of the product code tell Microsoft the source of the product. For example, the last five characters may tell Microsoft that the copy of XP you have was intended for a Dell Desktop computer. Windows may display an “Invalid Product Code” error if you try to install to a new Gateway computer, an XP operating system that came originally with a Dell Computer.

While the last 5 characters of the OEM versions prevent it from being installed on any computer, it's not true of copies you buy directly from

Microsoft or from retail stores. Those copies of Windows XP and Windows Vista can be installed on any computer, at least one time.

Microsoft began a “Windows Genuine Advantage” anti-piracy program in July 2005 that requires users to verify the authenticity of Microsoft programs. When installing an operating system like Windows XP or Vista, this means that your computer calls into Microsoft and connects with their database to confirm that you are using a valid copy of Windows.

If the copy of windows you're using has already been registered to another computer, Microsoft can know this and deny your installation. They'll display a warning that you have, “exceeded the maximum number of installations” for the product.

If you do succeed in installing a copy of XP, with or without hacks, you'll want to disable Microsoft automatic softare updates, so that if Microsoft decides that the copy of your operating system isn't authentic, they can't disable it remotely.

To disable Microsoft Automatic updates,

1. Click Start > Control Panel > Automatic Updates

2. Select the option, “Turn off Automatic Updates”


If you want to remove Microsoft Vista and replace it with Windows XP, the easiest solution is to by a legitimate copy from Microsoft or a legitimate seller. You can buy an authentication code immediately from Microsoft for $99. Or, expect to pay $70 to $100 for a retail version of Microsoft Windows XP.