I have a late 2015 iMac. I put my O/S on an external hard drive because the original drive had gotten extremely slow, and was afraid it was failing. I want to put Boot Camp on the external drive, to run Windows, but when trying to set it up, keep getting the message to remove all external discs. I there any way to put it on my external drive?
iMac 21.5″, macOS 12.6
Another alternative is to use the free VirtualBox virtual machine with a VirtualBox Windows guest stored on an external fast SSD. Then you can run Windows full screen concurrent with Monterey. I ran VirtualBox for years with Windows 10 like this. Then I purchased a 2020 27-in iMac with 1TB internal flash drive, and increased the RAM to 40 GB.
My RAM purchase (in 2022) from macsales had Parallel's Desktop Pro as part of the bundle and I found Parallel's guest features made VirtualBox look like a toy, and I now have all of my Parallel's guests (Ubuntu, Big Sur, Mojave, Windows 11 Pro) configured on an external Crucial X8 SSD (1050 MB/s) connected to my Thunderbolt 3 port on the iMac. I usually assign 8 threads (cpus) and 16 GB RAM to each guest. Parallels Desktop Pro annual subscription runs me $120USD.
If your iMac only has 8 GB RAM, then a Virtual Machine approach would not be advised.
officially it's not supported by bootcamp and not supported by microsoft even on non macs
but some manage to get it to work
read
Install Windows on a partition of externa… - Apple Community
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Installing Boot Camp on external hard drive.
