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I used to run a Boot Camp partition on my Macbook Air (Early 2015, Catalina). When I didn't need it anymore I deleted the partition using Disk Utility.

However, I noticed that when I boot up my Macbook while holding down option to show the boot drives, it shows my old Windows drive.

When I select it, it fails with the following screen:

I also did a full reinstall of Mac OS recently using Internet Recovery where I reformatted the entire drive. The Windows option still appears even after the reinstall, which means there are artifacts left over.

What's causing this behaviour? Where are these boot options stored and how would I go about deleting the Windows option?

Thanks!

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    Adding the macOS version and model of Mac might help here...
    – Steve Chambers
    Commented Dec 27, 2019 at 13:42

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The Microsoft bootloader program bootmgfw.efi is found in the EFI partition on disk either in the EFI/Boot directory, the EFI/Microsoft directory or both.

While it is acceptable (according to UEFI specifications) to have several EFI partitions both Apple and Microsoft expect there to be only one.

You say "I reformatted the entire drive" but unless you went to Disk Utility and actually overwrote the data with zeros you most likely didn't. It can be a bit convoluted to do this - see How to Secure Erase a Mac SSD / Hard Disk from Recovery Mode

What you likely did is take the option in the macOS installer to reinstall. This deleted the partition tables and then the installer created new partitions including a new EFI partition with exactly the same start and end positions - macOS will always create a 200MiB EFI partition from sector 40 to sector 409639. As macOS doesn't generally use the EFI partition whatever was there before will miraculously be there again.

To remove the straggling MS files first delete any Microsoft directory in the EFI partition:

  • disable SIP as described here How to Disable System Integrity Protection (rootless) in Mac OS X
  • create mount point for EFI partition with mkdir /Volumes/ESP
  • mount EFI partition with sudo mount -t msdos /dev/disk0s1 /Volumes/ESP
  • check if MS directory is still there with ls /Volumes/ESP/EFI/Microsoft
  • delete it with sudo rm -r /Volumes/ESP/EFI/Microsoft
  • delete EFI/Boot too if it exists with sudo rm -r /Volumes/ESP/EFI/Boot
  • alternatively delete everything except for the EFI/APPLE directory using Finder and empty the trash.

Finder

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  • There are a lot of inaccuracies in your answer. The idea that the EFI partition would be created with the old data still intact is not true. The idea of replication by using the gpt is not valid since the gpt command is non destructive with respect to the contents of a partition. All the gpt remove command does is set the partition type id to 0 and update the CRC32 values.
    – David Anderson
    Commented Dec 27, 2019 at 20:25
  • @DavidAnderson - I have often deleted and recreated partitions (and sometimes the whole partition table) using various tools. If the start and (less importantly) the end positions remain the same I can assure you that the data is preserved. As the Windows recovery screen is definitely not part of macOS and is definitely stored on disk perhaps if you have a more convincing answer as to how it could survive a reinstall you should post it :) Nonetheless I take your point about replicating with gpt and I'll edit it out. It was not a good example and rather tangential anyway.
    – lx07
    Commented Dec 27, 2019 at 20:49
  • Well, I posted my answer over 4 years ago.
    – David Anderson
    Commented Dec 27, 2019 at 22:05
  • So you believe a new EFI partition was created and this partition was not formatted? I would contend that once the EFI partition was created, the partition would be FAT32 formatted. This would remove all entries that may have existed in the root folder (directory), therefore would be no EFI folder (subdirectory) with other files and folders (subdirectories). I would assert the OP did not erase (reformat) the entire drive. Instead, the OP erased (formatted) the macOS partition, leaving the EFI partition intact.
    – David Anderson
    Commented Dec 27, 2019 at 22:06
  • I post the previous comment knowing that when Apple software allocates space on a drive (which can be a partition), the beginning of the space is overwritten. This occurs even if this space is a partition that will be formatted.
    – David Anderson
    Commented Dec 27, 2019 at 22:06

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