Question: Recently, a new drive with letter Z showing up which cannot be opened to see what’s inside. Here is the picture for better understanding.

screenshot

How to fix it? Sometimes, restarting system fixes temporarily.

Right click menu:

right click on drive shows up this

Disk Management view:

It shows the unknown drive without the drive letter and says it is EFI something. It again says it is empty but right click on drive shows it is not empty. Am just guessing with the drive size. So, it could be different drive too. Please look at the following picture for understanding.

disk management view of my HDD

P.S. I have upgraded to Windows 10 from Windows 8.1

Answer: Courtesy of this thread on the Microsoft Technet Forums, I found the following Powershell solution:

$CimPartInfo = get-partition foreach ($CimPart in $CimPartInfo) { ?if ($CimPart.Guid -eq $null) { ?$PartGUID = [regex]::match($CimPart.AccessPaths, ‘Volume({[^}]+})’).Groups[1].Value ?} ?else { ?$PartGUID = $CimPart.Guid ?} ?”Volume GUID $PartGUID” ?”`tDisk # ?:`t$($CimPart.DiskNumber)” ?”`tPartition #:`t$($CimPart.PartitionNumber)” ?”`tDriveLetter:`t$($CimPart.DriveLetter)”} #foreach CimPart

It ll print something likes this:

Volume GUID {6c747513-0000-0000-0000-100000000000} ?Disk # ?: ?0 ?Partition #: ?1 ?DriveLetter:Volume GUID {6c747513-0000-0000-0000-f01500000000} ?Disk # ?: ?0 ?Partition #: ?2 ?DriveLetter: ?CVolume GUID ?Disk # ?: ?0 ?Partition #: ?0 ?DriveLetter:Volume GUID {6c747513-0000-0000-0000-20023b000000} ?Disk # ?: ?0 ?Partition #: ?4 ?DriveLetter: ?UVolume GUID {6c747513-0000-0000-0000-20823b000000} ?Disk # ?: ?0 ?Partition #: ?3 ?DriveLetter:

You can also cross-reference the GUID with the output of mountvol Z: /L to verify.

In your case it is most likely the EFI System Partition. On UEFI installations, it contains the Windows Boot Manager and its BCD (Boot Configuration Data) store �C by default, at least.

You can remove the drive letter like this:

mountvol z: /d

You can read more about the mountvol command here.