After users disputed his count, a Microsoft executive explained how the company concluded that the upcoming Windows 7 is the seventh version of the operating system.

On Tuesday in the US, Mike Nash, vice president of Windows product management, followed up a Monday announcement that Microsoft had settled on Windows 7 by defending his tally.

"There's been a lot of lively discussion since I confirmed yesterday that the official name for the next version of the Window client operating system will be 'Windows 7' about how we got to the number '7'," said Nash in an entry to the Windows Vista blog. "I'll say up front, that there are many ways to count the releases of Windows and it's been both a trip down memory lane and quite amusing to read all the different theories about how we got to the number."

In fact, others had wondered that same thing. On Monday, bloggers as well as users commenting on Nash's announcement arrived at different numbers when ticking off each edition of Windows. The AeroXperience blog, for example, counted seven as of Windows Vista, eight if the consumer-oriented Windows Millennium was included. Also on Monday, Windows blogger Ed Bott came up with seven for Windows 7 by counting only members of the NT family, starting with Windows NT 3.1. "If you try to count using the consumer versions from the Windows 9X family, or the barely usable Windows 1 and 2 releases, you'll quickly go mad," Bott added.

Nash, however, did count Windows 1.0 and 2.0, the versions Microsoft launched in 1985 and 1987, respectively, to get to seven for Windows 7. "Anyway, the numbering we used is quite simple. The very first release of Windows was Windows 1.0, the second was Windows 2.0, the third Windows 3.0," he said. "[But] here's where things get a little more complicated."

To reach the magic number, Microsoft tossed all Windows 9x versions -- Windows 95, 98, 92 SE and Millennium -- as Windows 4.0. By that reckoning, Windows 2000 is 5.0 and Vista is 6.0.

Windows XP -- still the most-used version of Windows by a wide margin -- was relegated to the minor 5.1 by Microsoft. "[When] we shipped Windows XP as 5.1, even though it was a major release, we didn't' want to change code version numbers to maximize application compatibility," Nash explained.

Some users called Nash's logic confusing. "Wow. That makes total sense. Not," said someone identified only as "joemaruschek" yesterday in a comment on the Vista blog.

"I've been programming Windows for 13 years and don't know whether to laugh or shake my head when reading this post," said another user, "PatriotB."

Others were bewildered, but still feel the Windows 7 name was a good pick. "I'm still not entirely sure on how the numbers work out, but I like the name anyway," said "StophVista."

To confuse matters further, Nash noted that although the next Windows will carry the "7" moniker, and is considered the seventh version of the operating system, its code will actually be marked as Windows 6.1. "We decided to ship the Windows 7 code as Windows 6.1, which is what you will see in the actual version of the product [when you run] cmd.exe," Nash said.

"There's been some fodder about whether using 6.1 in the code is an indicator of the relevance of Windows 7. It is not," he continued. "The only thing to read into the code versioning is that we are absolutely committed to making sure application compatibility is optimized for our customers."