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Is there a way to assign permissions to a regular user to access a physical device/drive on Windows?

The idea is to bypass "error: Cannot open the raw disk '\.\PhysicalDrive1'. Otherwise, it looks like I might have to disable UAC and run everything as an Administrator, which isn't ideal!

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The question should be re-phrased as:

Why would a regular user want to use raw device to boot a VM?

You should ask the person to create a virtual hard disk to boot a VM, not use an existing Windows operating system to boot a VM. That could cause damage or disk corruption to the current OS.

Please ask the person to create a virtual hard disk in the user's My Virtual Machines folder.

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In short you can't easily. Here's why:

Using PowerShell we can get the ACLs for a physical "raw" disk drive:

PS C:\> [io.directory]::GetAccessControl("\\.\PHYSICALDRIVE1") | Format-List


Path   :
Owner  : BUILTIN\Administrators
Group  : NT AUTHORITY\SYSTEM
Access : Everyone Allow  ExecuteFile, ReadAttributes, ReadPermissions, Synchronize
         NT AUTHORITY\RESTRICTED Allow  ExecuteFile, ReadAttributes, ReadPermissions, Synchronize
         NT AUTHORITY\SYSTEM Allow  FullControl
         BUILTIN\Administrators Allow  FullControl
Audit  :
Sddl   : O:BAG:SYD:(A;;FX;;;WD)(A;;FX;;;RC)(A;;FA;;;SY)(A;;FA;;;BA)

So only SYSTEM and Administrators have permissions that allow write access to the drive defeating your initial request.

There seem to be third party tools (such as User-mode Raw Disk Access) that work around this but it doesn't seem to be something that Microsoft were intending to support on fixed (non-removable) disks. See https://support.microsoft.com/en-us/kb/942448 for Microsoft's take.

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