Having successfully ran Fedora 23 from an external HD (on a Win7 laptop) for several weeks, the Linux OS (or the HD) failed. One fix suggested by a web trawl was to try booting with UEFI mode disabled in the BIOS, which didn’t work. But! Having UEFI mode disabled allowed me to install Fedora on my Windows volume, whereas this was an issue in the past – I didn’t have to change from MBR to GUID partition table. I simple shrank the Windows partition to free up 200GiB and let Linux install itself. Fedora 23 installed without a hitch, and I am now running a true dual boot system. And thanks to Justin Yang, I now have access to Arduino, Processing and Supercollider using the realtime kernel and Jack for low latency audio.
Oh, and all my various Arduino boards and clones work perfectly (apart from my agéd NG sad face). Bring on Pure Data.