The rumor started with the authoritative headline “60% of Windows Vista Code To Be Rewritten“. Although the article doesn’t offer any detailson how the 60% estimate was reached, the story quickly spread. I agree with Alec Saunders’ assertion that this figure is hogwash.

The argument against 60% is simple – Let’s assume for a second that Windows Vista has 10 million lines of code, and that this alleged rewrite will occur through the end of 2006, 280 days from now. 10,000,000 / 280 ~= 36,000 lines of code per day! It is simply not possible to write, let alone debug, let alone regression test this volume of code.

There is real discussion to be had about the devolving feature set (WinFS!) and release date of Vista, but the 60% story is unlikely and unsubstantiated.