According to company documents filed with the US Securities and Exchange Commission, Microsoft's client division, which includes Windows operating systems products for desktop and notebook PCs, generated operating income of $2.48bn (£1.57bn) on revenue of $2.89bn for the quarter to the end of September.
The company said, "Windows is intellectual property that resulted from billions of dollars of research and development and product design to develop a product that delivers tremendous value to customers and partners."
A Microsoft representative said the operating system had been a major driver of PC growth, both in the business community and among users.
The software giant also rebuffed critics who claimed that the price of Microsoft's operating system had not come down as quickly as that of the PCs on which it runs.
The company said developments in the latest version of Windows "dramatically" improved productivity over Windows 9x products.
"Windows XP is dramatically different from previous consumer operating systems such as Windows 95, 98 and ME. Windows XP includes far more feature and functionality that customers ever had before or had to pay for separately," the company said.