2

I messed up my partition table after trying to get Windows 7 Boot Camp installation bootable after being unbootable using option/alt on start up.

Back Story

At some point a few months ago, I had issues with my partition table after migrating to APFS. I can't exactly remember what happened, but I messed up my partition table. I followed instruction here. It successfully resolved the partition table for Mac OS, which was my urgent concern at the time. Around the same time, my Bootcamp became unbootable. I'm assuming something I did while trying to fix my partition table made bootcamp unbootable. When I boot into Windows using opt/alt on startup, I get "No bootable device -- insert boot disk and press any key" error. However, Windows still boots using Parallels on Mac OS without issue. I had been using this as a work around until I could resolve the issues with bootcamp.

Broken Partition Table

I started out this morning with a working Mac OS X and non-bootable Bootcamp partition. Boot camp would boot in Parallels, but not via System Preferences/Start Up Disk or option/alt on start up. In Disk Utility, it showed bootcamp was not bootable from the inspection panel. I tried to do several things to resolve the issue in Windows 7 including check disk, start up repair, etc. Upon further research, I found that the issue appears to related to the Protective MBR.

I installed a trial of Paragon Hard Drive Manager. It had some features that I thought might resolve my issues via a graphical interface. I disabled SIP. I ran "Correct BCD" and "Correct Bootcamp Boot Record" functions. Both seemed to run, with little output. I restarted and tried to run bootcamp from alt/option. Same error as before - no bootable device.

Next, I tried following the steps here. I rebooted. I tried to launch bootcamp from alt/option - same error. After booting back into Mac OS, I launched Paragon Hard Drive Manager. It said I needed to "resync" the partitions. I had stumbled upon gptsync from another post, and I assumed that's what the software was going to do. I clicked okay and that's when I first noticed disk0s4. I'm guessing something between these two steps created this extra partition.

I seem to have really screwed up my Partition table now. In Disk Utility, I can see disk0s4, which is a duplicate of my Mac OS APFS. Though, it's FAT32, not APFS. I only have a 1 TB drive, yet somehow I have two 848 GB partitions. I think it's just an additional entry in the partition table.

I still have the Mac running in Mac OS as I write this, but I'm afraid to reboot as I don't think it will come back up until I remove this extra FAT32 partition. It's no longer booting into Mac OS because it rebooted over night (unknown to me as to why). I also still haven't resolved the bootcamp issue - making the bootcamp partition bootable from opt/alt on start up.

Current Partition Information

$ sudo gpt -r -vv show /dev/disk0
gpt show: /dev/disk0: mediasize=1000555581440; sectorsize=512; blocks=1954210120
gpt show: /dev/disk0: PMBR at sector 0
gpt show: /dev/disk0: Pri GPT at sector 1
gpt show: error: bogus map
gpt show: unable to open device '/dev/disk0': Undefined error: 0
$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                 Apple_APFS Container disk1         848.3 GB   disk0s2
   2:       Microsoft Basic Data                         848.6 GB   disk0s4 << Unknown partition
   3:       Microsoft Basic Data BOOTCAMP                152.0 GB   disk0s3

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +848.3 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD            796.6 GB   disk1s1
   2:                APFS Volume Preboot                 53.0 MB    disk1s2
   3:                APFS Volume Recovery                510.5 MB   disk1s3
   4:                APFS Volume VM                      1.1 GB     disk1s4

/dev/disk2 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        +21.0 MB    disk2
   1:        Apple_partition_map                         32.3 KB    disk2s1
   2:                  Apple_HFS rEFIt                   20.9 MB    disk2s2
# From Mac OS Recovery Mode on 1-11-2021
# used a flash drive to attempt to run the command from the comments
# copy the output. I was able to manually run it
bash-3.2# -bash-3.2# diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:       Microsoft Basic Data                         848.6 GB   disk0s1
   2:       Microsoft Basic Data BOOTCAMP                152.0 GB   disk0s2
/dev/disk1
<ADDITIONAL INFORMATION ABOUT RECOVERY PARTITION OMITTED>

-bash-3.2# diskutil info disk0
   Device Identifier:        disk0
   Device Node:              /dev/disk0
   Part of Whole:            disk0
   Device / Media Name:      APPLE SSD SM1024F Media

   Volume Name:              Not applicable (no file system)

   Mounted:                  Not applicable (no file system)

   File System:              None

   Content (IOContent):      GUID_partition_scheme
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 PCI
   SMART Status:             Verified

   Total Size:               1.0 TB (1000555581440 Bytes) (exactly 1954210120 512-Byte-Units)
   Volume Free Space:        Not applicable (no file system)
   Device Block Size:        512 Bytes

   Read-Only Media:          No
   Read-Only Volume:         Not applicable (no file system)
   Ejectable:                No

   Whole:                    Yes
   Internal:                 Yes
   Solid State:              Yes
   OS 9 Drivers:             No
   Low Level Format:         Not supported

-bash-3.2# diskutil info disk0s0
Could not find disk: disk0s0
-bash-3.2# diskutil info disk0s1
   Device Identifier:        disk0s1
   Device Node:              /dev/disk0s1
   Part of Whole:            disk0
   Device / Media Name:      Basic data partition

   Volume Name:              

   Mounted:                  No

   File System Personality:  MS-DOS
   Type (Bundle):            msdos
   Name (User Visible):      MS-DOS (FAT)

   Partition Type:           Microsoft Basic Data
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 PCI
   SMART Status:             Verified
   Disk / Partition UUID:    7C89FB14-3E93-4F24-EF45-9C1F793F62DF

   Total Size:               848.6 GB (848555933184 Bytes) (exactly 1657335807 512-Byte-Units)
   Volume Free Space:        0 B (0 Bytes) (exactly 0 512-Byte-Units)
   Device Block Size:        512 Bytes

   Read-Only Media:          No
   Read-Only Volume:         Not applicable (not mounted)
   Ejectable:                No

   Whole:                    No
   Internal:                 Yes
   Solid State:              Yes

-bash-3.2# diskutil info disk0s2
   Device Identifier:        disk0s2
   Device Node:              /dev/disk0s2
   Part of Whole:            disk0
   Device / Media Name:      Untitled 2

   Volume Name:              BOOTCAMP

   Mounted:                  Yes
   Mount Point:              /Volumes/BOOTCAMP

   File System Personality:  NTFS
   Type (Bundle):            ntfs
   Name (User Visible):      Windows NT File System (NTFS)

   Partition Type:           Microsoft Basic Data
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 PCI
   SMART Status:             Verified
   Volume UUID:              D003F722-F8D8-404F-806C-6C88C3EAC665
   Disk / Partition UUID:    F7571F70-5458-4FF7-BBFB-BBC700DFD95E

   Total Size:               152.0 GB (151999479808 Bytes) (exactly 296873984 512-Byte-Units)
   Volume Free Space:        18.0 GB (18020077568 Bytes) (exactly 35195464 512-Byte-Units)
   Device Block Size:        512 Bytes
   Allocation Block Size:    4096 Bytes

   Read-Only Media:          No
   Read-Only Volume:         Yes
   Ejectable:                No

   Whole:                    No
   Internal:                 Yes
   Solid State:              Yes

-bash-3.2# diskutil info disk0s3
Could not find disk: disk0s3
-bash-3.2#
# Update using latest Mac OS Recovery mode - 1/12/2021
-bash-3.2# /Volumes/VonNeumann/help.txt 
1+0 records in
1+0 records out
512 bytes transferred in 0.000793 secs (645471 bytes/sec)
\M-b(\M-2\^A\M-FJWH\^A\0\0\0\0\0\0\0/P\M^N\0\0\0\0\0\^A\0\0\M^@\0\0\0\0NXSB\0\
\^P\0\0\M-{UX\f\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\^B\0\0\0\0\0\0\0\M-L](\
B\M-"\M^XI\M-@\M-2G\M-4S\M^^g{\M^Cc\M^C\M-\\0\0\0\0\0000P\M^N\0\0\0\0\0\^X\^A\
\0\0Pl\0\0b\M^B\^Q\^D\0\0\0\0f\M-K\^P\^D\0\0\0\0\M^U\0\0\0\M-H\s\0\0\M^S\0\0\0\
\^B\0\0\0|\s\0\0L\0\0\0\M^VP\n\0\0\0\0\0\M-KY\^R\0\0\0\0\0\^A\^D\0\0\0\0\0\0\0\
\0\0\0d\0\0\0\^C\^D\0\0\0\0\0\0\M^IP\n\0\0\0\0\0\M^KP\n\0\0\0\0\0T\M-y\n\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\
\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\

Disk: /dev/disk0    geometry: 121643/255/63 [1954210120 sectors]
Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
 1: EE    0   0   2 - 1023  89   4 [         1 - 4294967295] <Unknown ID>
 2: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
-bash-3.2# diskutil info /dev/disk0
   Device Identifier:         disk0
   Device Node:               /dev/disk0
   Whole:                     Yes
   Part of Whole:             disk0
   Device / Media Name:       APPLE SSD SM1024F

   Volume Name:               Not applicable (no file system)
   Mounted:                   Not applicable (no file system)
   File System:               None

   Content (IOContent):       GUID_partition_scheme
   OS Can Be Installed:       No
   Media Type:                Generic
   Protocol:                  PCI
   SMART Status:              Verified

   Disk Size:                 1.0 TB (1000555581440 Bytes) (exactly 1954210120 512-Byte-Units)
   Device Block Size:         512 Bytes

   Media OS Use Only:         No
   Media Read-Only:           No
   Volume Read-Only:          Not applicable (no file system)

   Device Location:           Internal
   Removable Media:           Fixed

   Solid State:               Yes
   Virtual:                   No
   Hardware AES Support:      No

-bash-3.2# diskutil info /dev/disk0s0
Could not find disk: /dev/disk0s0
-bash-3.2# diskutil info /dev/disk0s1
   Device Identifier:         disk0s1
   Device Node:               /dev/disk0s1
   Whole:                     No
   Part of Whole:             disk0

   Volume Name:               
   Mounted:                   No

   Partition Type:            Microsoft Basic Data
   File System Personality:   MS-DOS
   Type (Bundle):             msdos
   Name (User Visible):       MS-DOS (FAT)

   OS Can Be Installed:       No
   Media Type:                Generic
   Protocol:                  PCI
   SMART Status:              Verified
   Disk / Partition UUID:     7C89FB14-3E93-4F24-EF45-9C1F793F62DF
   Partition Offset:          512 Bytes (1 512-Byte-Device-Blocks)

   Disk Size:                 848.6 GB (848555933184 Bytes) (exactly 1657335807 512-Byte-Units)
   Device Block Size:         512 Bytes

   Volume Total Space:        0 B (0 Bytes) (exactly 0 512-Byte-Units)
   Volume Free Space:         0 B (0 Bytes) (exactly 0 512-Byte-Units)

   Media OS Use Only:         No
   Media Read-Only:           No
   Volume Read-Only:          Not applicable (not mounted)

   Device Location:           Internal
   Removable Media:           Fixed

   Solid State:               Yes
   Hardware AES Support:      No

-bash-3.2# diskutil info /dev/disk0s2
   Device Identifier:         disk0s2
   Device Node:               /dev/disk0s2
   Whole:                     No
   Part of Whole:             disk0

   Volume Name:               BOOTCAMP
   Mounted:                   Yes
   Mount Point:               /Volumes/BOOTCAMP

   Partition Type:            Microsoft Basic Data
   File System Personality:   NTFS
   Type (Bundle):             ntfs
   Name (User Visible):       Windows NT File System (NTFS)

   OS Can Be Installed:       No
   Media Type:                Generic
   Protocol:                  PCI
   SMART Status:              Verified
   Volume UUID:               D003F722-F8D8-404F-806C-6C88C3EAC665
   Disk / Partition UUID:     F7571F70-5458-4FF7-BBFB-BBC700DFD95E
   Partition Offset:          848555933696 Bytes (1657335808 512-Byte-Device-Blocks)

   Disk Size:                 152.0 GB (151999479808 Bytes) (exactly 296873984 512-Byte-Units)
   Device Block Size:         512 Bytes

   Volume Total Space:        152.0 GB (151999475712 Bytes) (exactly 296873976 512-Byte-Units)
   Volume Used Space:         134.0 GB (133979398144 Bytes) (exactly 261678512 512-Byte-Units) (88.1%)
   Volume Free Space:         18.0 GB (18020077568 Bytes) (exactly 35195464 512-Byte-Units) (11.9%)
   Allocation Block Size:     4096 Bytes

   Media OS Use Only:         No
   Media Read-Only:           No
   Volume Read-Only:          Yes (read-only mount flag set)

   Device Location:           Internal
   Removable Media:           Fixed

   Solid State:               Yes
   Hardware AES Support:      No

-bash-3.2# diskutil info /dev/disk0s3
Could not find disk: /dev/disk0s3
-bash-3.2# 
# Update with Mac OS running: 1-12-2021
$ diskutil unmount disk0s3
Volume BOOTCAMP on disk0s3 unmounted
$ sudo dd if=/dev/disk0s3 count=1 | hexdump -Cv
1+0 records in
1+0 records out
512 bytes transferred in 0.000316 secs (1620742 bytes/sec)
00000000  eb 52 90 4e 54 46 53 20  20 20 20 00 02 08 00 00  |.R.NTFS    .....|
00000010  00 00 00 00 00 f8 00 00  3f 00 ff 00 00 f0 c8 62  |........?......b|
00000020  00 00 00 00 80 00 80 00  ff ef b1 11 00 00 00 00  |................|
00000030  00 00 0c 00 00 00 00 00  02 00 00 00 00 00 00 00  |................|
00000040  f6 00 00 00 01 00 00 00  87 99 b4 e6 b8 b4 e6 16  |................|
00000050  57 e9 a5 e2 fa 33 c0 8e  d0 bc 00 7c fb 68 c0 07  |W....3.....|.h..|
00000060  1f 1e 68 66 00 cb 88 16  0e 00 66 81 3e 03 00 4e  |..hf......f.>..N|
00000070  54 46 53 75 15 b4 41 bb  aa 55 cd 13 72 0c 81 fb  |TFSu..A..U..r...|
00000080  55 aa 75 06 f7 c1 01 00  75 03 e9 dd 00 1e 83 ec  |U.u.....u.......|
00000090  18 68 1a 00 b4 48 8a 16  0e 00 8b f4 16 1f cd 13  |.h...H..........|
000000a0  9f 83 c4 18 9e 58 1f 72  e1 3b 06 0b 00 75 db a3  |.....X.r.;...u..|
000000b0  0f 00 c1 2e 0f 00 04 1e  5a 33 db b9 00 20 2b c8  |........Z3... +.|
000000c0  66 ff 06 11 00 03 16 0f  00 8e c2 ff 06 16 00 e8  |f...............|
000000d0  4b 00 2b c8 77 ef b8 00  bb cd 1a 66 23 c0 75 2d  |K.+.w......f#.u-|
000000e0  66 81 fb 54 43 50 41 75  24 81 f9 02 01 72 1e 16  |f..TCPAu$....r..|
000000f0  68 07 bb 16 68 70 0e 16  68 09 00 66 53 66 53 66  |h...hp..h..fSfSf|
00000100  55 16 16 16 68 b8 01 66  61 0e 07 cd 1a 33 c0 bf  |U...h..fa....3..|
00000110  28 10 b9 d8 0f fc f3 aa  e9 5f 01 90 90 66 60 1e  |(........_...f`.|
00000120  06 66 a1 11 00 66 03 06  1c 00 1e 66 68 00 00 00  |.f...f.....fh...|
00000130  00 66 50 06 53 68 01 00  68 10 00 b4 42 8a 16 0e  |.fP.Sh..h...B...|
00000140  00 16 1f 8b f4 cd 13 66  59 5b 5a 66 59 66 59 1f  |.......fY[ZfYfY.|
00000150  0f 82 16 00 66 ff 06 11  00 03 16 0f 00 8e c2 ff  |....f...........|
00000160  0e 16 00 75 bc 07 1f 66  61 c3 a0 f8 01 e8 09 00  |...u...fa.......|
00000170  a0 fb 01 e8 03 00 f4 eb  fd b4 01 8b f0 ac 3c 00  |..............<.|
00000180  74 09 b4 0e bb 07 00 cd  10 eb f2 c3 0d 0a 41 20  |t.............A |
00000190  64 69 73 6b 20 72 65 61  64 20 65 72 72 6f 72 20  |disk read error |
000001a0  6f 63 63 75 72 72 65 64  00 0d 0a 42 4f 4f 54 4d  |occurred...BOOTM|
000001b0  47 52 20 69 73 20 6d 69  73 73 69 6e 67 00 0d 0a  |GR is missing...|
000001c0  42 4f 4f 54 4d 47 52 20  69 73 20 63 6f 6d 70 72  |BOOTMGR is compr|
000001d0  65 73 73 65 64 00 0d 0a  50 72 65 73 73 20 43 74  |essed...Press Ct|
000001e0  72 6c 2b 41 6c 74 2b 44  65 6c 20 74 6f 20 72 65  |rl+Alt+Del to re|
000001f0  73 74 61 72 74 0d 0a 00  8c a9 be d6 00 00 55 aa  |start.........U.|
00000200

Additional Context

I have Paragon NTFS installed. It also causes issues in which Bootcamp won't show up. I have disabled write access to circumvent this issue. I have homebrew installed, which is how I installed gdisk. I'm a software engineer whose comfortable with the CLI, just unfamiliar with partitions tables.

Notes

  • MacBook Pro 15" Mid 2014
  • Mac OS 10.14.6
  • Windows 7
  • Add to your question the output from the command for i in {1..4}; do echo $i; diskutil info disk0s$i | grep -e Disk\ Size -e Offset; done. Hopefully, this will document where the partitions are on the drive. – David Anderson Jan 11 at 6:49
  • When I run that, I get 1\n2\n3\n4\n - basically it iterators through, but there's no info from diskutil. Unfortunately, somehow my Mac died in the middle of the night and it didn't come back up. I had to boot into recovery and open terminal from there to run this command. – technogeek1995 Jan 11 at 17:04
  • I was able to run the command for diskutil info manually. I updated the question with the results. It seems my APFS disk0s1 is gone now. – technogeek1995 Jan 11 at 17:14
  • The command did not work because you booted to an older version of OS X or macOS Recovery. I should have thought of that. Try posting the output from the command export LC_CTYPE="ASCII" followed by sudo dd if=/dev/disk2 skip=409640 count=1 | vis -cfw; echo. Also try the command sudo fdisk /dev/disk0. Note the sudo may not be needed. – David Anderson Jan 11 at 22:07
  • Did you mean for the dd command to be disk2? – technogeek1995 Jan 11 at 22:31
1

The output given in the OP's question can be use to reconstruct the GPT. Once reconstructed, the output from the gpt -r show /dev/disk0 command should appear as shown below.

      start       size  index  contents
          0          1         PMBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6         
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640 1656926168      2  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
 1657335808  296873984      3  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
 1954209792        295     
 1954210087         32         Sec GPT table
 1954210119          1         Sec GPT header

You should be able to boot to macOS Recovery (Option-Command-R at startup) and enter the following commands to reconstruct the GPT.

Note: You may need to start each command with a sudo, as in sudo dd if=/dev/zero count=34 of=/dev/disk0.

diskutil unmountdisk disk0
dd if=/dev/zero count=34 of=/dev/disk0
dd if=/dev/zero seek=1954210087 count=33 of=/dev/disk0
gpt -f create -f disk0
gpt -f add -i 1 -b 40 -s 409600 -t efi disk0
gpt -f add -i 2 -b 409640 -s 1656926168 -t apfs disk0
gpt -f add -i 3 -b 1657335808 -s 296873984 -t windows disk0

If the partitions have not been corrupted, then you should be able to boot macOS. If successful, then I will update this answer with instructions for fixing the MBR partition table.

Fixing the MBR Partition Table

Boot to macOS Recovery and enter the following command. (The sudo may not be needed.)

sudo fdisk -e /dev/disk0

The the -e option makes the fdisk command interactive. The input is given below.

e 1
ee
n
1
1657335807
e 2
7
n
1657335808
296873984
f 2
q
y

Afterwards, the output from sudo fdisk /dev/disk0 should be similar to the output shown below.

Note: Only the #, id, start and size columns have to match your output.

Disk: /dev/disk0    geometry: 121643/255/63 [1954210120 sectors]
Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
 1: EE    0   0   2 - 1023 254  63 [         1 - 1657335807] <Unknown ID>
*2: 07 1023 254  63 - 1023 254  63 [1657335808 -  296873984] HPFS/QNX/AUX
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused      

When finished, boot back to macOS.

Update Windows 7 Boot Data and Code

Note: Windows 10 can produce boot data and code that is compatible with Windows 7. You probably can substitute a Windows 7 installer flash drive, but I have only tested this answer by using Windows 10.

  1. Insert the Windows 10 installer flash drive in a USB port on the Mac. Instructions for creating the Windows 10 installer flash drive is given the next section.

  2. Start or restart the Mac and immediately hold down the option key until the Mac Startup Manager icons appear. Select the external drive icon with the label EFI Boot.

  3. If the message "Press any key to boot from CD or DVD" appears, press any key.

  4. When the image shown below appears, press the shift+F10 key combination to open a Command Prompt window.

  5. Enter the following commands.

    attrib c:\boot\bcd -s -h -r
    del c:\boot\bcd
    bcdboot c:\windows /l en-us /s c: /f bios
    bootsect /nt60 c: /mbr
    exit
    
  6. Select Next, then Repair your computer and finally Turn off your PC.

  7. After the Mac turns off, remove the flash drive.

How to Create the Windows 10 Installer Flash Drive

Note: This flash drive will not be used to install Windows 10.

  1. Download the latest 64 bit Windows 10 ISO file from the Microsoft website Download Windows 10 Disc Image (ISO File). This is a free download.

  2. Use the Disk Utility application to erase an 8 GB or larger flash drive. Enter the following in the popup.

  3. Use the Finder application to mount the downloaded Windows 10 ISO file.

  4. Use the Finder application to copy all the files in the mounted volume to the flash drive.

  5. Use the Finder application or Disk Utility application to eject the mounted Volume.

(Optional:) How to Remove the Windows Boot Manager at Startup

This section outlines several methods to remove the following screen from appearing at startup.

  • Method 1

    You can use this method if the Mac boots to Windows 7 after 30 seconds without user intervention.

    Left click on the Start Menu button, then right click on Computer and select Properties, as shown below.

    Click on Advanced system settings, as shown below.

    Under, Startup and Recovery, click on the Settings button, as shown below.

    Uncheck Time to display list of operating systems:. The result is shown below.

    Click on the OK button.

  • Method 2

    Boot back to the Windows 10 installer flash drive and enter the commands given below.

      attrib c:\boot\bcd -s -h -r
      del c:\boot\bcd
      bcdboot c:\windows /l en-us /s c: /f bios
      exit
    
  • Method 3

    Open an Administrator: Command Prompt window. Enter the bcdedit command. In my case, the results are shown below.

    In this case, the second Windows Boot Loader entry needs to be removed. The command bcdedit /delete {identifier} will do this. In this case, the command would be entered as shown below.

     bcdedit /delete {70613c75-5568-11eb-807e-97d1c8053bbf}
    
  • 1
    Can you post the output from the command diskutil unmount disk0s3, followed by sudo dd if=/dev/disk0s3 count=1 | hexdump -Cv. You need to enter the commands while booted to macOS. – David Anderson Jan 13 at 0:42
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    The macOS operating system does not include the /usr/standalone/i386/boot0 file. This is true for every version of OS X and macOS released by Apple. The means you can not use macOS alone to replace the boot code in the MBR. (The MBR is the first sector on the drive.) In your case, you erased this boot code when you issued the dd if=/dev/zero count=34 of=/dev/disk0 command. You will be replacing this boot code when you issue the bootsect /nt60 c: /mbr command. See here. – David Anderson Jan 13 at 20:16
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    The Appendix of this answer gives the source code for the MBR boot code used by Microsoft. The source code of fdisk, where this error message occurs, is given here. You can see that fdisk will substitute zeros for the missing boot code. Therefore, when fdisk is used to reinitialize the MBR boot code, fdisk actually erases the MBR boot code. – David Anderson Jan 13 at 21:03
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    I updated my answer. See chat for more information. – David Anderson Jan 14 at 0:37
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    These steps worked excellent. Thank you again. I would highlight to others in the future, one Windows 7 boot instance was activated and the other was spamming warnings about not being activated. I ended up deleting the non-activated one and have had no issues since. – technogeek1995 Jan 14 at 16:06

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