Windows 10 – 0xC1900101 – 0x20017 error

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Windows 10 – 0xC1900101 – 0x20017 error

I am using my Lenovo T420S now since more than four years. This notebook is still comparable to current machines that are now on sale. It is equipped with a I7 processor and 16GB of RAM. In addition I added two Samsung SSDs during the years. I haven´t found any significant better notebook of that quality level since I started to look for a new one in this summer. So I decided to still stay with the T420 since there is a lot better one on the market that is worth its price. Best on that decision I had to trying to get Windows 10 working on that machine.

After several (> 10) tries I was finally able to upgrade to Windows 10. Me was confronted with an always occuring 0xC1900101 – 0x20017 error, after the system rebooted for the first time during installation (before the actual upgrade starts). In my case, the T420 rebooted and a start up screen with the Windows logo is shown. After a couple of seconds a single white dot was shown in the lower middle of the screen (should have been a loading spinner). After rebooting, Windows 7 is restored and the following error code is shown:

The installation failed in the SAFE_OS phase with an error during BOOT operation.

To avoid a long try and error marathon for you, you just might have to follow the steps I am listing below. It might be, that not all of the steps are necessary to perform. I am sorry, but I tried several steps with each installation attempt. So, you can just check, if a subset helps you.

  1. Use the windows media creation tool to download the Windows 10 upgrade directly to an USB stick from which the installation can start later on.
  2. When installation starts and you are asked if you would like to update the installation software, you should do it.
  3. Finally I went to change some BIOS settings and those are the ones that enabled me to install Windows 10.
    1. Config > Display
      1. Boot Display Device: Thinkpad LCD
      2. Graphics Device: Discrete Graphics
      3. OS Detection for NVIDIA Optimus: Disabled
    2. Config > Power
      1. Intel Speedstep technology: Disabled
      2. CPU Power Management: Disabled
      3. PCI Express Power Management: Disabled
    3. Config > CPU
      1. Core Multi-Processing: Disabled
      2. Intel Hyper-Threading Technology: Disabled
    4. Security > Memory Protection
      1.  Execution Prevention: Disabled
    5. Security > Virtualization
      1. Intel Virtualization Technology: Disabled
      2. Intel VT-d Feature: Disabled
    6. Security > I/O Port Access
      1. All to disabled, expect of Ethernet LAN and eSATA Port to update the Windows installation software before the update
    7. Startup
      1. UEFI/Legacy Boot: Both
      2. UEFI/Legacy Boot Priority: UEFI First
      3. Reserve memory for UEFI Boot Manager: Enabled

With theses settings in the BIOS I was now able to install Windows 10 to my machine. After the installation finished, you can set back all settings to their original state, expect the Config > CPU > Core Multi-Processing that needs to stay in the state „Disabled“.

From my current point of knowledge, the Core Multi-Processing is not effecting the actual active cores of the CPU, but is just some kind of „combining“ multiple cores to process a single thread. On my notebook this isn´t affecting the speed of the machine at all.

After installing Windows 10 I recommend to install software updates from Lenovo to your system. There are for instance new drivers for the NVIDIA Optimus.


  1. Tomas 11. August 2015 at 23:27 - Reply

    Hello, I was trying to upgrade my T420s to W10 as well and ran into the same error. Just one question, if you enable Core Multi-Processing after the upgrade the laptop won’t boot at all?

    Thanks for the article.


    • Sven Seiler 14. August 2015 at 15:54 - Reply

      Currently I have the Core Multi-Processing disabled as any of the settings regarding the CPU or virtualizing led to not booting anymore.

  2. Tobi 22. August 2015 at 18:30 - Reply

    Yes!!! Yes!!! I got the same problem over and over again. Tried a lot of things but nothing worked for me. Now upgrade is done.My T420s is working well under WIN 10. Thanks a lot for the BIOS settings. You absolutly made my day. :-).

  3. Eirik 8. September 2015 at 22:20 - Reply

    Regarding this part:
    Core Multi-Processing: Disabled
    Intel Hyper-Threading Technology: Disabled

    If you leave the Hyper-Threading disabled it works with Core Multi-Processing. (Tried and tested on T420s)

    This is after the Windows 10 upgrade is completed.

    • Sven Seiler 13. September 2015 at 11:34 - Reply

      Hey Eirrik,
      is it still working even after some reboots?
      I will give it a try again, but in my case the system wasn´t booting anymore after I enabled the core multi-processing.
      It might be, that one of the comprehensive Windows 10 updates in the last month fixed the error?

      BR and thank you for your feedback

  4. Bernhard Plattner 9. September 2015 at 10:37 - Reply

    Thank you so much for giving the hint about disabling various functions in the BIOS. This not only saved the day, but also the week :-).
    After finally succeeding with the installation of Win 10 on the T420 (with almost everything disabled) I re-enabled the features set by set. In the end I found that only enabling the Intel VT-d feature prevents the system from booting. On my machine with BIOS 83ET76WW, version 1.46, also Core Multi-Processing is now enabled and does not interfere.
    Strangely enough on one of my other machines (a Lenovo X201 Tablet) Win 10 boots without problems even with Intel VT-d enabled.

    • Sven Seiler 13. September 2015 at 12:16 - Reply

      Thank your for the feedback. It is great to hear, that until now some of the issues seem to be solved with Windows updates.
      I will check again, if I can re-enable VT-d and Core Multi-Processing, as Eirik mentioned.

    • Thomas Pluempe 24. Dezember 2015 at 14:01 - Reply

      For me it’s the same on the W520. When I switch VT-d back on, Win10 gets stuck during boot, much like the Win10 installer did. It turns out that it works fine for others on the W520 and it looks as though this might be down to them having a different CPU. Mine is an i7-2720QM, it worked fine e.g. on a i7-2760QM with reset-to-standard BIOS settings (including VT-d on), see discussion of this here:

      I’d be interested to hear what CPUs with VT-d on have shown the „0xC1900101 – 0x20017 error“ and which didn’t. Bernard, Sven, what CPUs have you got?

      • Bernhard Plattner 26. Dezember 2015 at 20:32 - Reply

        This is part of the output of msinfo32, showing the T420 model, processor type and properties:
        System Model 4180P74
        System Type x64-based PC
        Processor Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz, 2701 Mhz, 2 Core(s), 4 Logical Processor(s)
        BIOS Version/Date LENOVO 83ET76WW (1.46 ), 05.07.2013

  5. Thomas Pluempe 16. Dezember 2015 at 21:13 - Reply

    Thanks so much, Sven. I have been trying and failing for a while to install Windows 10 on a Thinkpad W520 and although your instructions are for a T420s I figured they are probably similar enough that this will work for me, too, and indeed it did.

    • Sven Seiler 23. Dezember 2015 at 16:39 - Reply

      You are welcome. I thought that there might be others dealing with this error for a while, so I decided to write it down.

  6. Gerson Riddy 24. Dezember 2015 at 09:22 - Reply

    Good one Thomas very helpful. I have got my T420 up and running on W10 using the above. Many thanks!

  7. Jonathan 28. Januar 2016 at 11:32 - Reply

    Most appreciated.
    On an early reboot during the upgrade, I received an „operating system missing“ message with a „hosed‘ upgrade.
    The OS had been destroyed!
    I then restored the original W7 installation and followed your BIOS changes, and the upgrade went through fully this time.

  8. Kevin 25. Juli 2016 at 16:37 - Reply

    Had exactly the same issue with my T420s. After reading this article, I noticed i was still running on an old BIOS version (1.33) and after upgrading to 1.41, dated 4.3.2016 (from the official Lenovo Support site) Windows 10 setup finally completed fine.

  9. Rita Li 17. November 2018 at 15:38 - Reply

    I have a L420 with exactly same error message received when Win 10 upgrade first tries to reboot, even BIOS settings is not exactly the same but following this article by changing Config >CPU > Core Multi Processing to Disabled is the key for a successful reboot & finally with Win 10 upgraded all fine, Thank you Sven for writing this up, you make my day!

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