You can buy Windows 7 Ultimate 64-bit from Microsoft's official website or other authorized retailers. This will ensure you receive a legitimate, licensed copy with support and updates.

If you're looking to install a new operating system, I recommend considering a newer version of Windows, such as Windows 10 or Windows 11. These versions receive ongoing support, security updates, and feature enhancements.

If you're looking for a free and open-source alternative, you can consider various Linux distributions (e.g., Ubuntu, Linux Mint, Fedora) that offer similar functionality to Windows.

To help you with your original query, I'll provide some general text: