I noticed something unusual when booting up Windows 8.1 this morning. A new disk partition is created. Local Disk (Z)

See below enter image description here

I have gone through many sites related to the problem and found quite a few similar issues. Although this one seems to be different according to me. The drive is inaccessible despite me being the administrator. I've tried viewing the contents of the drive by various means but still in vain.

Strangely so, the partition is in fact occupied and allocated to a few hundred megabytes. About 143MB free of 256MB.

I ran an antivirus scan using Bitdefender,took a screenshot of this scan window and noticed this: if you look closely into the screenshot you can see the file path z:\efi\hp\boot\es-es\bootmgr.exe.mui

Obviously it has something to do with the EFI boot partition and my OEM HP.

I haven't performed any driver update or BIOS modification for a few months so I can't point to a specific culprit.

Can you guys help? Thanks!

  • 2
    The Bitdefender window is blocking all useful information. Here is my guess Windows assigend a drive letter to the EFI partition. Just unmount the partition. How do I mount the EFI partition on Windows 8.1 so that it is readable and writeable? – Ramhound May 9 '16 at 16:18
  • @Ramhound changed the screenshot – Ashwin May 9 '16 at 16:23
  • Just because you are an Administrator does not mean you actually have permissions to the files and folders located on the drive. Your inability to do so is actually expected given the permissions of the drive. Windows Explorer itself, by default, does not have elevated permissions. What you are trying to do requires the Windows Explorer process permissions to be elevate to acomplish. – Ramhound May 9 '16 at 16:28
  • @Ramhound How do I elevate privileges of Windows Explorer? – Ashwin May 9 '16 at 16:37
  • The answer to the duplicate of this question explains how to do that. – Ramhound May 9 '16 at 16:44

It looks like the mystery partition is in fact an OEM partition from HP, which was previously hidden but for some reason assigned a drive letter. To get rid of the drive in my computer open the disk management console from start menu, right click on the partition and there is an option to configure the drive letter. Open that and there is an option to remove it completely. This will not delete the partition, but it will be invisible to your Windows. You shouldn't worry about what's on it, after you remove the drive letter if any virus tries to access it it would fail.


I had the same thing on my HP, I use Auslogics Boostspeed and ran its registry defrag on next boot. It created a restore point and then local disk(z) showed up, after a reboot it defragged the registry and disk(z) was gone then everything got loaded. My guess is it was a temporary back-up of the registry.

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