[Solved] Disabling VT-x/AMD-v on Windows 10

[LusitaniaU20]

Hello. I am trying to set up a Windows 95 VM on my Windows 10 host. I have successfully installed it, however, whenever it shows the "Windows 95 is starting for the first time" message, it shortly after crashes to a black screen, and gives me the following error: "While initializing device IOS: Windows protection error. You need to restart your computer." On every tutorial I have checked, it says that this error message is caused by having System>Acceleration>Enable VT-x AMD-v on. They also say that disabling this option will fix the problem. However, I cannot find this option. There is a similar one, under the Processor tab, called "Enable Nested VT-x/AMD-v" but it is by default disabled, grayed out, and I'm not sure if the Nested part makes a difference. I believe the tutorials I am using use VBOX version 5.x and I am using version 6.1. Is there any way I can get around this problem without having to downgrade to version 5?

I have seen a similar question before, however it was for Mac OS X, not Windows 10, and there was no satisfactory answer.

[pt58]

Check out the following :

viewtopic.php?f=28&t=9918#p422192

[mpack]

However, I cannot find this [VT-x] option.

That's because it's no longer optional.

There is a similar one, under the Processor tab, called "Enable Nested VT-x/AMD-v" but it is by default disabled, grayed out, and I'm not sure if the Nested part makes a difference.

It makes a huge difference. That new option is to do with making VT-x/AMD-v visible to the guest, it has nothing to do with whether the host software requires VT-x/AMD-v (it does).

[LusitaniaU20]

Thank you! I applied the patch and my VM is working now.

[mpack]

Good to hear it, thanks for reporting back.

[Digika]

That's because it's no longer optional.

Correct me if I'm wrong but you are saying that in this current toggled off and disabled state as on the attached screenshot, "Nested VT-x/AMD-V" is enabled by default for the virtualization capabilities?

[mpack]

Read the topic above.

[Digika]

What topic above? The only "topic: in this thread is this:
viewtopic.php?f=28&t=9918#p422192
and it is not relevant to my question.

If you don't want to answer the question you could just say so. Next time when you make confusing changes to the product make sure you communicate their new state in a more meaningful way so the users wont have to look for the answers randomly.

[mpack]

The "topic above" is this topic, i.e. the posts above yours that you skipped over in order to ask a question that was already answered very explicitly.

And - I have made no changes to anything. This is a user discussion forum, I am not a dev.

[Digika]

I've read that answer before asking my question, which still stands.

[multiOS]

Why not just read the VirtualBox Manual Section 9.33 ( Page 294 in Version 6.1.10 )? It answers your question. The most recent changes to the nested virtualisation feature were also formally announced by 'Oracle' in the Change Log when Version 6.1.0 was first released, so the developers did communicate those changes with anyone willing to read.

[scottgus1]

you are saying that in this current toggled off and disabled state as on the attached screenshot, "Nested VT-x/AMD-V" is enabled by default for the virtualization capabilities?

No.

The layout of VT-x/AMD-V usage in Virtualbox goes like this:

Host PC BIOS/CPU VT-x/AMD-V setting > Host OS > Virtualbox > Enable VT-V/AMD-V > Guest OS

In old pre-6.1.x Virtualbox there was an "Enable VT-x/AMD-V" checkbox on the Acceleration tab.
The host might or might not have VT-x/AMD-V in its BIOS/CPU, and if it was not there the guest could only be 1-processor 32-bit Windows 8 or earlier. If you wanted to have 2 or more processors, 64-bit, or Windows 8.1 or later, you needed to have VT-x/AMD-V on in the host PC BIOS/CPU, and the "Enable VT-x/AMD-V" must have been checked, so the Virtualbox guest environment could use VT-x/AMD-V to run 2-core 64-bit.

In 6.0.x, an additional "Enable Nested VT-x/AMD-V" checkbox appeared on the Processor tab. This allowed the additional capability of not only allowing Virtualbox to use VT-x/AMD-V to run multi-core 64-bit, but to allow the guest's OS to use VT-x/AMD-V for its own purposes.

6.1.x took out the ability to not have VT-x/AMD-V on the host PC BIOS/CPU. Now you must have VT-x/AMD-V on the host PC, and therefore VT-x/AMD-V will always be available for Virtualbox to use to run multi-core 64-bit in the guest environment. So there is no longer a need to have the "Enable VT-x/AMD-V" checkbox on the Acceleration tab. However, the "Enable Nested VT-x/AMD-V" checkbox remains on the Processor tab.

To summarize, "Enable VT-x/AMD-V" and "Enable Nested VT-x/AMD-V" are two different functions, they do not equal each other.

"Enable VT-x/AMD-V" is on all the time in 6.1.x & later.

If "Enable Nested VT-x/AMD-V" is grayed out, either your host PC is not capable of passing VT-x/AMD-V into the guest OS, or your host BIOS/CPU does not have VT-x/AMD-V turned on, or something else, like Hyper-V is using VT-x/AMD-V, so Virtualbox can't use it.

[mpack]

[are you] saying that ... "Nested VT-x/AMD-V" is enabled by default for the virtualization capabilities?

There is a similar one, under the Processor tab, called "Enable Nested VT-x/AMD-v" but it is by default disabled, grayed out, and I'm not sure if the Nested part makes a difference.

It makes a huge difference. That new option is to do with making VT-x/AMD-v visible to the guest, it has nothing to do with whether the host software requires VT-x/AMD-v (it does).

What part of that discussion is confusing for you?

[fth0]

@scottgus1:
A very detailed and good explanation, probably worth keeping.

I only have a remark / enhancement request to your last paragraph. I'd replace

your host PC is not capable of passing VT-x/AMD-V into the guest OS

by

the host CPU is missing capabilities that VirtualBox needs to provide VT-x/AMD-V to the guest OS