Windows 10 Dev 20277.1 fe_release 201207-1545

Good Morning, friends! Microsoft has released a new Windows 10 pre-build number 20277 for Windows Insider program members using the Dev channel (formerly “Early access”).

Full build number: Windows 10 Dev 20277.1 fe_release 201207-1545


Starting today, insiders on the Dev channel can get builds from the RS_PRERELEASE branch. They will appear in Windows update if you manually check for updates. This means that insiders need to independently confirm the installation of the build from the RS_PRERELEASE branch. Now the insiders can install the Assembly 21277. After that, you will continue to get an update from the RS_PRERELEASE.

If you want to leave everything as it is, you will continue to automatically receive builds from the FE_RELEASE branch until the company transfers all insiders on the Dev channel to the RS_PRERELEASE. It will happen after the holidays. The company still needs insiders who use builds from the FE_RELEASE branch to provide feedback on them. So it’s okay if you decide to stay on these builds.

Be sure to verify out the listing of discovered issues. It is important to note that the lists of fixes and associated bugs differ for the FE_RELEASE and RS_PRERELEASE builds.

Important! After you decide to install an Assembly from the RS_PRERELEASE branch, you can’t go back to getting assemblies from the FE_RELEASE, because the device will have a higher system build number. You can go back to the previous version of the system within ten days if you don’t install another build from the RS_PRERELEASE branch during this time.

We would let you that the Dev channel which can contain quite unpleasant with errors if you are a beginner. If you need more establishment, we recommend switching to the Release Preview channels or Beta (Late access).


  • They have fixed an issue that could cause the WinRE volume label to disappear after multiple updates.
  • They have also fixed an issue where apps might not update, giving an error code 0x80073D02.

Known Error

  • We investigate reports that the system update process may hang for a long time when trying to install a new build.
  • The real-time preview for pinned site tabs is not yet available to all insiders, so you can see a grey window when you hover over the thumbnail on the taskbar. Engineers are working to improve this feature.
  • Engineers are working on enabling a new taskbar feature for already pinned websites. However, you can unpin a site from the taskbar, remove it from the edge://apps page, and then re-pin it.
  • We are investigating reports that some users experience an error code 0×80070426 when using their Microsoft account to log in to various applications. If you encounter this problem, then restart your device, which should help.
  • We are investigating an issue where after installing this build, the “Settings” -> “System” -> “memory” -> “disk and volume Management” section does not display any disks. As a workaround, you can use the classic disk management tool.

I wish you a successful update!

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