Microsoft released Windows 10 Build 21387 to the Slow Ring last evening, and it shows that a couple of items on the task manager have been removed, and there is a new one added. The first difference is the removal of Internet Explorer from the task manager, which is a good thing considering that the browser has not been updated since January 2016. The second thing is the addition of a new tab called “Perf”, which shows an Energy usage graph for the CPU, GPU, Disk, Network, and Memory of your PC. For more information on how to blog, see the following blog posts: Online Course Blogger Blogging Course

Turns out, there was a bug in the previous Windows 10 build that caused the Task Manager to throw a fit. Now, build 21387 has dropped Internet Explorer from it’s Advanced menu, and that’s a good thing. Sure, it’s a bit disappointing that Microsoft is no longer supporting the legacy browser, but it’s also the right call—and it’s actually a good sign that the company’s going to be more aggressive about phasing out older, less secure software in general.

This Friday, Microsoft is rolling out Windows 10 build 21387 for Insiders in the Dev channel. As already announced, Internet Explorer 11 is no longer preinstalled. But to our surprise, another feature has been removed from the operating system – the Eco Mode option in the task manager. alt=Windows Insider banner width=600 height=357 data-ezsrc= /> Eco mode allows you to identify applications that use a lot of resources. Eco mode can be used to reduce the resource consumption of such an application so that the system prioritizes other applications. However, it is not included in the Windows 10 build 21387, as the developers want to refine the experience and fix some issues they learned from the feedback. As for Internet Explorer 11, Microsoft has already announced that it will be removed from the default package of Windows 10. Support for Internet Explorer 11 ends on the 15th. June 2021. The company cited three main reasons for replacing the old browser with the new Microsoft Edge: better compatibility, optimized performance and improved browser security. Here are the changes in today’s Insider Preview release.

What’s new in Windows 10 Build 21387

Changes and improvements

  • With this Insider Preview release, the Internet Explorer 11 desktop application has been taken out of service. For more information, see
  • We’re disabling the Eco Mode feature in Task Manager to improve performance and address some issues that have emerged from feedback from Windows Insiders.


  • We fixed an issue where the Times New Roman font was unexpectedly used during the upgrade and on the welcome screens that appeared after the initial login.
  • We fixed an issue where some Insiders were getting errors when trying to run Notepad from the Run dialog box.
  • We have fixed an issue for WSL users that caused some Linux GUI applications to not run correctly from the automatically added shortcut to the Start menu.
  • We fixed an issue that was causing the PIN reset or change workflows to not work.
  • We have fixed an issue where the night light was immediately turned off by some Insiders after it was turned on.
  • In recent flights, we’ve fixed an issue that caused you to unexpectedly receive the error message We can’t find an audio device when trying to play audio from a connected Bluetooth speaker.
  • We fixed an issue where explorer.exe could crash after repeatedly using the touchpad gesture to change the virtual desktop.
  • We have fixed two issues affecting the ability to print to USB printers.
  • We have fixed an issue where the Windows Update page was not responding after you clicked the Stop Update button.
  • We have fixed an issue that caused some devices to freeze with error code 0xc1900101. Although this patch fixes the problem on some devices, there is a second problem that causes the same error code (see below). We are also working on a solution to this problem.
  • We fixed an issue where some devices were repeatedly offering the .NET update after installation. After installing this version, you will not be prompted to update .NET. If you are having trouble getting 21387 through a pending .NET update, you can get around this by pausing the paused updates and then canceling them.
  • We have fixed an issue that was causing some devices to crash with a DPC_WATCHDOG_VIOLATION error when using OneDrive Personal Vault.
  • We fixed the ctfmon.exe error when using ATOK (third-party IME) when performing the conversion in some Win32 applications.

Known issues

  • Currently, the Windows Camera application does not respect the default brightness settings set on the new camera settings page.
  • We are currently investigating an issue that causes search items (including the file explorer search bar) to no longer display correctly in a dark theme.
  • We are investigating an issue that can sometimes cause a pop-up window to appear after clicking the taskbar button in the upper left corner of the screen.
  • We are working on a fix for the second issue, which caused some devices to get error code 0xc1900101 when upgrading to this version. If the update fails, it reverts to the previous version. If you experience this problem, we recommend that you suspend updates until we release a version with a fix.

If you have set your device to receive updates from Dev Channel/Fast Ring, open Settings – > Update & Recovery and click the Check for Updates button on the right. Allows you to install the latest available Insider Preview version of Windows 10. Please support us. Winaero is really counting on your support. You can help the site continue to provide you with interesting and useful content and software by using these options: By Sergiy Tkachenko on 21. May 2021, last update 21. May 2021 on Windows 10.

About Sergei Tkachenko

Sergey Tkachenko is a Russian software developer who founded Winaero in 2011. In this blog Sergey writes about everything related to Microsoft, Windows and popular software. Follow him on Telegram, Twitter and YouTube.