mfelker wrote: On occassion after I install an OS in a VM I may wish to install it on thke host. I suppose there could be a way to do that directly from the ISO but have a diks is muchi easier for me at least.
If you want to do a physical install then burning an ISO Image to optical media is necessary however, under normal circumstances it just is not necessary to burn an ISO Image to optical media to do a virtual install. Additionally to do so is an utter waste of time not only because one would have to take the time to unnecessaraly burn it to optical media, it also takes considerably longer to install from optical media then directly from an ISO Image! 
In all the years I've been doing this there are basically 3 primary reasons why one has trouble booting from an ISO Image, the least of which the image is not bootable and or quite often the CD/DVD is not set to be connected and or probably the most often reason is a corrupted download despite however it was downloaded saying it was successful (even if by omission) and in fact it wasn't and the User didn't validate the checksum. Additionally in the case of the latter I find once in a while the User is combative or resistive to preforming the checksum and eventually they come back and admit it was corrupted. It is probably ignorance induced fear of not knowing and or understanding how to preform the checksum along with the use of a Command Prompt/Terminal.