The product key for Windows 7 is usually supplied on the certificate of authenticity that is supplied with every pre loaded Windows 7 laptop or computer. The bit size would depend on the computer configurations as well. The product keys vary accordingly. Usually original users do not need to worry about the bit size or any other specification of the product key. Every original or licensed purchase of Windows 7 comes with a unique product key. However, if you are unable to read the product key number on the sticker that comes with your laptop, you might look for a free download of the same. This is possible through authorized sites of Windows. If you are downloading the same through other sites, remember that you will only find trial versions.
The ultimate 64 bit versions of Windows 7 ultimate are available on many download sites for free. It can be accessed to get the software reinstalled or reloaded on your computer.
If you opt for a free download of the product key it would be active for a limited time period. You could use the same till you recover the original product key on your computer or laptop if you are an authorized user.