No dual boot option on Windows 7 desktop install of Zorin Core

[ntp]

1. Installed Try version of Core (Nvidia drivers) from USB flash drive onto Intel i5 desktop running Windows 7 Home Premium. Worked fine
2. So decided to install dual boot version via external WP Passport 2TB drive.
3. Installation to external disk worked fine to a point, but then crashed at the end (sorry no screens).
4. When trying to re-install, no dual boot option appears. Install doesn't see Windows drives at all. Can only install a full wipe Core from USB flash drive now.

Has Zorin installed something permanent on my Windows machine (boot grub?) that is preventing a dual boot option from appearing?

Windows loads and runs fine normally.

[337harvey]

Zorin needs to overwrite the windows boot efi partition with grub in order to offer the dual boot option. If it is installed anywhere else (Grub) it won't offer the Windows as an option.

I normally use the something else method to install, which provides you the opportunity to create partitions and choose which one to install the grub menu to. If the device is chosen, and not a partition, it may create another partition for grub (or use another if comparable size). I don't like this "feature" of the unity installer.

You may want to check out the tutorials section where I did a write up for this. It is explained better there as well as a full walkthrough:

[HOW TO] Partition & Install Zorin 16

This step-by-step guide will allow you to partition your hard drive (HDD, SSD, NVMe) so that installation goes a little more smoothly. This will work for a multi-boot system as well, but you will have to resize your Windows partition first and you will be using the Windows Boot Manager EFI partition instead of creating one. Otherwise, partitioning is pretty much the same. Please be sure to perform the steps in Before You Install prior to attempting any of these changes. Mistakes and rushing …

[ntp]

Thanks very much @337harvey , it sounds a bit too complicated for me to take on right now. I was hoping just to install a quick Zorin dual boot option for those times when I want to use Linux for something. Disk partitioning has always been a mystery to me.

[337harvey]

Partitioning is like organizing your file cabinet with a few dividers that have a specific purpose. You have an idea what those areas will hold. You can even name them should you want to. The folders that go inside are for the EFI, OS, and a virtual drive for storage or like the /home folder, a specific purpose.

Knowing this, the mystery that is partitioning is not a intimidating. It's a matter of permanent organization for the OS you run. It's important but something most users do not have to interact with, so can be daunting. Should you want to tackle this, let me know and we can walk through it, with little effort this can be changed.