Unknown drive appearing in File Explorer, "SYSTEM (Z:)"

  1. Ten Seconds's Avatar
    Posts : 11
    Windows 10 Home, Windows 7 Ultimate

    Unknown drive appearing in File Explorer, "SYSTEM (Z:)"

    Hi guys, using Windows 10 Home, 64 bit.

    Never before in my time of using Windows computers have I seen this before. Today, as I browsing through my files, I noticed in the left pane of the Windows Explorer window that another "hard drive" or, for all I know, "partition", has appeard in the list of available disk drives. It's name is "SYSTEM (Z:)" and I have no clue how it got there. It's a 356 MB file system, FAT32, defined as "Local Disk", and apparently has about 75 MB already used. I tried looking at it using diskmgmt.msc and it shows it as a 360 MB partition in my main drive that is hosting the OS. It is NOT the recovery partition. It also doesn't have the aforementioned "Z:" designation that the Explorer displays. It also, as you can see, doesn't have a name, either. See attached photo:
    Unknown drive appearing in File Explorer, "SYSTEM (Z:)"-dlefkeu.png

    Here's another look at the main drive using EASEUS Partition Master. This time, the actual name "SYSTEM" displays itself:
    Unknown drive appearing in File Explorer, "SYSTEM (Z:)"-ufxepju.png

    Anyone know why this is showing up? And can I just delete the partition and merge the free space? Or will that mess up any OEM factory install stuff? I want OEM files to remain. I just know that this WAS NOT here earlier.

    Does anyone know?
      My Computer

  2. Gort's Avatar
    Posts : 46
    Windows 10

    Below is what I wrote in another forum when a poster asked a similar question. It's very late at night here and I'm just about to go to bed, so decided to cut and paste what I wrote there, changing the necessary details. Whatever you do, don't delete that partition. Below is what I wrote on how to hide that partition (remove its given drive letter).

    That's your EFI partition, which is the partition used to initiate the booting process of the OS(s) you use on the machine. It's normal that the partition exists and you shouldn't, unless you know what you're doing, mess with it. Still, it shouldn't really have been made visible and given a drive letter.

    Why it got a drive letter is a bit of a mystery. It happened to me when I upgraded from Windows 8.1 to 10, but I fixed it using Windows own diskpart (Disk Manager wasn't enough to solve this). Is it harmful to keep it as it is? Not really, but it's annoying that a drive letter gets taken by it.

    The following might be daunting, so do this only if you feel confident, but it's not that difficult if you follow the advice to the letter. I can't stress this too much, but backup your system with a backup utility or, at the very least, the files you deem important. The EFI partition is critical and if broken will make your machine unbootable, so think seriously if you want to carry on.

    Here's a How-to Geek link describing the process: How to Use the Diskpart Utility to Assign and Remove Drive Letters

    Basically, open a Command Prompt as admin.

    Type in "diskpart" (no quotes) and then hit the enter key.

    You'll want to tell diskpart which volume (partition) to change, but first you'll need to find that volume, so you type in "list volume" (no quotes... and any further quotes by me you can ignore) and hit enter. This will, as the name suggests, list the volumes on your disk.

    Now find out which volume shows as your drive Z: and the number that it has been assigned in diskpart, then type "select volume N", where N is the number that the volume was given, and hit enter. This tells diskpart that you want to apply the changes to that particular volume.

    Now to double-check that you're on the right volume, type in "list volume" and check where the asterisk is. If it's beside the volume you wish to change, then good, if not you'll need to do "select volume N" again.

    Now, when you're sure you're on the right volume, type in "remove letter=Z" and hit enter, which should remove the drive letter.

    Check it has been done by typing "list volume" to see the results.

    Close the command prompt window. All done.
      My Computer

  3. Ten Seconds's Avatar
    Posts : 11
    Windows 10 Home, Windows 7 Ultimate
    Thread Starter

    Gort said:
    THANK YOU! I appreciate you taking the time to go and find your post about this, glad I'm not the only one who had a problem like this. Normally, I know the EFI partition is supposed to be in charge of managing boot order and execution, but since it decided to make itself visible (still don't know why, gonna think on it) I was a little worried that my installation may have been compromised in some way. Since it was visible and the used space on the partition was very different than the EFI partition on my Windows 7 machine, it had me a tad worried. You helped confirm that it wasn't what I thought it was.

    That info pertaining to DISKPART really helped and solved the creepy visible EFI partition from showing up. Thank you so much!
      My Computer

  4. Gort's Avatar
    Posts : 46
    Windows 10

    No problem. Glad it worked. :)

    Yes, it's a mystery why it happens. As I said in the post, it happened to me when I upgraded from Windows 8.1 to 10. Maybe the Anniversary Update for Windows 10 or subsequent update could have been the cause in your case. Still, that's just a guess.
      My Computer

  5. stuarttunstall's Avatar
    Posts : 302
    Windows 10

    My new HP notebook has the same "Z" drive, just appeared for some reason... Thanks for the explanation, as it is only small I am not worried about it, even less now I know what it is :)
      My Computer

  6. Posts : 1
    Windows 10 pro 64

    This Z: could appear when all restore points are gone for some reason. Could be a warning to create one. So when I saw the new Z: drive, I checked my RP list (with CC Cleaner), it was empty, I created one and the new Z: was gone without messing around with settings registry or anything else. So check your RP list before doing anything complicated or risky.
      My Computer

  7. jumanji's Avatar
    Posts : 5,613
    Windows 10 Home 64bit Version 20H2
      My Computer


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