The mod uses VirtualBox, a free open source virtual machine software to run operating systems such as Windows 95.
Inside Minecraft so you can create virtual hard disks to install operating systems from ISO files.
Of course, the community Minecraft started experimenting with mod VM Computers and someone managed to do Doom to run inside Minecraft. Of course with the new feature we will see a lot more. You could for example play it Minecraft on a computer inside Minecraft.
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