A leading tech analyst has put together a graphic showing that the ratio of Windows-based computers to Macs has tightened dramatically and is closer than it has been in a decade and a half.

Analyst Horace Dediu of Asymco has been following the Mac-PC war for years and recently crunched the numbers to show that, in 2011, Microsoft’s PC desktops and laptops outsold Apple’s Macs by a less-than 20-to-1 ratio.

It’s the lowest margin since 1996 and is roughly the same as 1985, shortly after the Mac was first released. And it’s significantly tighter than in 2004, the PC’s high-water mark, when it was outselling Macs by a ratio approaching 60-to-1.

Factor in mobile gadgets like smartphones and tablets, where Apple has so far outshined Microsoft and you’ve got a playing field that, if not level, is certainly less tilted than it used to be.

The shift, Dediu wrote Wednesday, began in earnest in 2004.

“Although PC volumes continued to grow, they did so more slowly and the Mac grew faster,” he said in a blog post. “What coincided with this was the emergence of portable computing. The MacBook became easily differentiable as a “better” laptop. It was not faster, did not have more storage or any key metrics being used to sell PCs. It was just better as an integrated product.”

That’s been the biggest shift since the mid-90s, Dediu writes, when the success of Windows ’95 gave a similar boost to Microsoft. The PC advantage steadily climbed from 1995 to 2004, dipping only once in a 10-year span.

When iPhones, iPads and other mobile devices are factored in, Microsoft’s advantage sits at about 2-to-1, Dediu said, and the two could break even within the next two years.

It’s unclear how much he factored in Windows 8, Microsoft’s new operating system that will run on both PCs and portable devices with the goal of marrying them together into a seamless computing experience. But Dediu says that Microsoft’s evaporating lead could be bad news for the software company.

“The consequences are dire for Microsoft,” he wrote. “The wiping out of any platform advantage around Windows will render it vulnerable to direct competition. This is not something it had to worry about before.

“Windows will have to compete not only for users, but for developer talent, investment by enterprises and the implicit goodwill it has had for more than a decade.”

Source: CNN.com