Recover lost BootCamp Windows partitions on a Mac

I have installed several Windows 7 and 10 version on several of my Macs using Apple's Boot Camp feature.

Recently, I found that almost all of them have disappeared: I was not able to boot from them any more when I held down the option (alt, ⌥) key at startup - the Windows partitions would either not appear at all or not boot up.

The main reason in my case was that the MBR was reset to a plain GUID entry, and my Windows versions do not like that, because they cannot handle the EFI / GUID partition info that the Mac prefers. Why that even happened? Probably from repartitioning operations I frequently perform on my disks - and Apple's Disk Utility is quite ignorant of the needs to keep Windows bootable in this regard.

To fix that, the MBR partition info needed to get fixed, in order to make the Windows NTFS visible again to the Windows boot system.

The easy way

After writing this article initially, I learned that there is a Mac program, WinClone,  that can fix this issue with a few clicks, in case you do not want to mess with it yourself as shown below.

The hard way

I used iBored to edit the partition layout of each disk that contains a BootCamp partition from something like this:

Into this:

Note that this reduces the size of the first partition (you could as well change its size to the minimum, which is 33), and adds a new partition with the start and size matching what you can inquire using the Partitions window (see Disk menu):

This modification makes the Windows partition available in the MBR, and after that, I can boot again from it. And it won't mess with macOS booting because that uses the GUID partition info which isn't getting modified by this procedure (for more info, read my older article on using BootCamp on a non-startup disk).

When I use too many programs that I also maintain

This post has nothing particular of interest, I'm just venting because I need a break. Read on to understand why:

I'm very detail oriented when I program. And when I see a critical bug, I need to fix it right away. I get so hooked on it that I often go into long sessions, and I'll be miserable if I have to stop in the middle of it.

Now, here's an example of what often happens then:

I am working on a paid project for a client. It has to do with recovering data from a complex file structure.

The data structures are in binary format, so I need to be able to read the data inside.

Since I have my own disk editor, iBored, I start writing a template for this file format. Since iBored's template system is a work in progress, it naturally leads to me having to add new code to iBored to suit a particular new construct in the template syntax. So I add new code to iBored.

The template system uses RbScript so that I can perform calculations to decypher complex data structures. RbScript is fairly limited by default, though. For instance, there is no sort function.

Which means that I have to write a sort function in RbScript. I need a RbScript editor. Real Studio's own Script editor sucks enormously - it doesn't even have Undo. Fortunately, there is Arbed. It has a better RbScript editor.

While writing my script in Arbed, I notice that its syntax parser doesn't indent Interfaces correctly. I like to fix that. I can, because Arbed is another tool of mine.

The RbScript editor and syntax highlighter is coming from the open source class "CustomEditField", written by Alex Restrepo. He has stopped working on it. Coincidentally, I took over.

Thus I am working several hours on the CustomEditField open source project to fix its indentation code, which is fairly convoluted (partly my fault). Eventually I get this done.

Next I need to merge the fixes of the CustomEditField project into the Arbed project file. Naturally, I use Arbed for this.

Merging takes a while because I had recently added new features to CustomEditField directly in Arbed, without merging those improvements back into the open source version. Meaning that I have to merge some code from CEF to Arbed, and other code in the other direction. I have to do this carefully. But eventually, I get all the changes merged into both projects.

When I try to save the updated projects, Arbed gives me an error message: wrong id in block header.

Great. So I have to find this bug. Takes me another 2 hours. It was very very well hidden.

That's where I am as of writing this blog post.

Now, I can go back to merge the changes between the projects once again. Then I can hopefully continue writing the Sort function in RbScript, after which I can finish the iBored template to view the data so that I can write the code I'm getting paid for.

Programming is fun. But so exhausting when you care too much.