Windows 8 is Microsoft's biggest overhaul of Windows in more than a decade and the company's attempt to stay relevant and exciting in a world where mobile gadgets have started to overshadow personal computers.
"Hardware partners are doing great things to take advantage of the features," Gates added. "It'll be a big deal."
Microsoft will release Windows 8 on October 26 along with a new version of internet Explorer.
Gates responded to a question about Windows 8 during an AP interview about the Bill and Melinda Gates Foundation's key role in a new global campaign to eradicate polio.
Windows 8 will replace Windows 7 on practically all personal computers sold to consumers.
It features major changes in the way consumers interact with their machines, and versions of it will also run on tablet computers and smartphones.
Although Microsoft has grown into much more than a maker of computer operating systems - providing computer services to corporations and Xbox gaming machines to game enthusiasts - Windows still accounts for a significant chunk of the company's annual revenue.
In 2011, Microsoft's "Windows & Windows Live" division generated 27 per cent, or $19 billion, of the company's $69.9 billion in annual revenue.