This one is a heaping pile of speculation, rumor, tips and hearsay, so stick with me on this one.

Yesterday we brought you word that Microsoft had entered the RC escrow phase of development when it compiled build 7105. This is true, and we have some additional details regarding this situation that we’d like to share with you.

On April 4, Microsoft created two separate builds: Build 7105 and build 7077. Now, here’s where the information begins to get a little speculative. All along, Microsoft has been developing the 7000 series of code. Builds 7000, 7057 and 7068 have all come from this family. Now there’s a new version in town, 7105, created on the same day as yet another 7000 build. This points to a branched development of Windows 7.

Branching is a word that explains the process of duplicating a body of code into a parallel development, so software engineers can test changes to one codebase without disturbing the integrity of the other.

The question now becomes: Which codebase — 7105 or 7077 — becomes the release candidate? It is widely believed that build 7077, or an iteration, will be the RC. Yet it’s also believed that they’re close to identical (for now).

Here’s where we enter the 100% speculation zone and explain why:

The Engineering Windows 7 blog just had an update which discusses the Windows 7 upgrade experience coming from Vista and coming from pre-RC builds of Windows 7. They posted an exceptionally interesting picture:

What the hell is going on here?

Now, this picture was provided in the context of these bits of information:

The reality is that upgrading from one pre-release build to another is not a scenario we want to focus on because it is not something real-world customers will experience. During development we introduce changes in the product (under the hood) that aren’t always compatible with what we call “build-to-build” upgrade.  The supported upgrade scenario is from Windows Vista to Windows 7.

So when you try to upgrade a pre-RC build you will find that you’re not able to and setup will tell you and you can then exit gracefully.

This image demonstrates how a user can overcome the version check that would prevent an upgrade from a pre-RC build (7000, 7057, 7068, etc.) to the release candidate. Microsoft (with warnings) outlines how to change the highlighted number to read “7000″ so the pre-RC builds become eligible for upgrade. While all of that is very interesting, the “7100″ number all but proves the existence of build 7105 and tells us that the final version of Windows has to be in the 7100 line.

So what does happen with build 7105? First we must remember that Windows 7 is probably going for retail manufacturing in September. This is called RTM (release to manufacturing), and a company’s RTM copy represents the most stable and bug-free chunk of code the company could make on its timetable. This RTM copy gets sold the world over, so it has to be good and ready. How does a company ensure that their RTM is ready to roll? That’s where the branch comes in.

Many sources are savvy to the idea that build 7105 is the first of many builds in the RTM branch which will receive fixes for bugs discovered when the public tests the RC. Microsoft is going to receive a lot of crash telemetry from the public RC, and it must take the months of May through August to review the data and implement the fixes to these issues. Bug fixes do not always fix the problem, and they’re perfectly capable of spawning new ones. It makes sense, then, that Microsoft would test the fixes in successive iterations of the 7000 branch, and the ones that check out will be committed to shaping the branch of code being prepared for RTM: 7100. This logic all falls in line with the purpose of a code escrow phase, which halts feature development and limits code changes to the show-stopping bug stomping.

With all that said (and so we do not disappoint on our headline), we present a screenshot of the leaked build 7077:

Windows 7 build 7077.0.090404-1255

A final interesting thing to note. Observe the “About Windows” box and look at the parentheses that follows “Version 6.1″ on the second line. Do you notice that there’s no build string? The only other time the parentheses has only contained a version number is in build 7000, the only public release of Windows 7 to date. If you’re a user of build 7022, 7034, 7057 or 7068, try it for yourself: Type “winver” in the run box and take a look; there’s a full build string there, but on Windows 7 beta 1, it only says “Build 7000.” This is yet more proof that Build 7077 represents  code escrow and the fast approach of RC1.