I wanted to create a Windows 7 installation on a USB drive for my iMac, so I followed these instructions. Basically, they allow you to create a bootable USB drive with Windows installed on it without resolving to using boot camp. The internal drive on the iMac is not big enough to also hold a boot camp installation.
After creating the USB drive, I plugged it into my iMac, and opened the boot menu by holding the option-key during boot. But the USB drive was not shown as a boot option, only the internal hard disk.
But then I plugged the USB drive into a MacBook Pro, and this does display the USB disk as a bootable device.
Why doesn't my iMac show the USB drive as a boot option, when the MacBook does, and can I fix it?
My iMac specs are:
- Retina 5K, 27-inch, Late 2015
- 4GHz Intel Core i7
- 16GB RAM
- AMD Radeon R9 M395X 4096 MB
- Running macOS 10.12.2
The MacBook specs are:
- Retina, 15-inch, Early 2013
- 2,7 GHz Intel Core i7
- 16GB RAM
- Intel HD Graphics 4000 1536MB
- Running macOS 10.11.2
The USB is a 500GB USB3 Hard Disk (not SSD). The partitioning was done using a Windows 7 installation in running under VMWare Fusion 7.1.3 (on my MacBook).
Note I realized though, that I might not get this to work with Windows 7, as Windows 7 doesn't have USB3 support out of the box. Actually booting the USB on my MacBook results in a Blue Screen of Death. I might need to try Windows 10, but I don't have a source DVD or image.