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About us

What is Windows On Windows®?
Windows On Windows® is a series of videos, available on YouTube, that aims to investigate the development of various versions of the Windows® operating system, from its very first incarnation as Windows® 1.0, all the way up to present day Windows® 10. This is done through installing and using various "builds" - or testing versions - from each operating system's development process. So far, series exist that document the development processes behind Windows® 95 (Codename "Chicago"), Windows® XP (Codename "Whistler") and Windows® Vista (Codename "Longhorn").


How is Windows® developed?
The process that takes place within Microsoft that results in a shipped version of Windows® (and, sometimes, an unshipped version!) has been roughly the same for all versions released; generally, the following things happen.

1. The project specifications are set out. This generally encompasses things such as setting out which main features will be included and a projected release date.

2. Developer groups are created. The developer groups (known as "build labs"), which comprise Microsoft employees, work in parallel to each other, compiling "builds" (a build is just a particular version of the operating system being worked on that contains a certain selection of features - a bit like a "practice version" that can be tested out to see what works and what needs fixing). Each developer group might be tasked to work on different sections of the operating system, for example, "group 1" might be instructed to work on creating the media functionality that is needed. When a developer group has finished a build, they give it a number, such as "1456". (NOTE: A higher build number does not necessarily mean a later version of the operating system. For example, "group 1" might compile build 1456 on 13th May, whilst "group 2" could compile build 1395 on 15th May, and so on.) The development process is split into phases (technically known as "branches"); generally, alpha, beta, release candidate (RC) and release to manufacturing (RTM). Each branch contains a selection of builds that are numbered within a predefined, designated range (e.g. 1000-1099 for the alpha branch). This is to help more easily distinguish between builds originating from different branches.

3. Testers test the features developers have been working on. At various stages during development, select builds are chosen to send to testers inside Microsoft. The testers will install and use the build to check to see if anything is broken, or if there are any bugs. They will then feedback to the developers and this feedback will be used to fix and/or improve future builds. Usually, in the beta and RC branches, an "official" build is chosen from the selection of builds and this is shared with developers outside Microsoft and/or consumers themselves in order for it to be tested on a wide range of hardware. They will then feedback to the developers inside Microsoft and this feedback will be used to fix and/or improve future builds. Consumer testing of builds occurs much more frequently today than it ever did in the past, owing to Microsoft's Windows® Insider Program, introduced during the development of Windows® 10.

4. Developers incorporate feedback from testers and continue to compile new, improved builds. The exact number of builds compiled during development depends on a variety of factors but is strongly influenced by tester feedback. Newer builds may add additional functionality ready for testing, fix bugs found by previous testers, both, or more! Steps 3 and 4 are then repeated as many times as necessary, until all desired features and functionality are present and tested satisfactorily.

5. A single build is chosen to be the final version of the operating system. This only happens after extensive and thorough testing to ensure the security and stability of the build. It is then released to manufacturers so that they can install it on devices ready to be sold to consumers. This is known as the release to manufacturing (RTM) build. Consumers will also be able to buy the build to install on existing hardware a short time after manufacturers get it. The build will receive security and occasionally, functionality updates from Microsoft in accordance with its Windows® lifecycle policy.


What is the purpose of this forum?
This forum is designed to augment the video series, where you can discover more about the history of Windows®, explore the development processes discussed in the videos in further detail and ask/respond to any questions posed in relation to the videos or the builds therein.


What's next for Windows On Windows®?
For up-to-date news on upcoming videos and other information, check The Noticeboard in the forum and/or the YouTube channel.

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