I'm guessing (didn't try) it could be a slightly patched version that does actually halt the CPU when it has nothing to do, since DOS is well known for using up all the host CPU when run in a VM even when idle and leading to people writing utilities like this:
The "Running the CPU at 100 percent for too long can damage your computer." message is probably legal ass-covering, since any system that can't 100% CPU usage 24/7 is defective. Indeed, back when DOS was common, that's what it did to the CPUs of the time, as did other applications which used a polling loop instead of waiting for interrupts.
http://maribu.home.xs4all.nl/zeurkous/download/mirror/dosidl...
I also found this (somewhat amusing) page discussing the problem:
http://wiki.freedos.org/wiki/index.php/VirtualBox_-_Heat
The "Running the CPU at 100 percent for too long can damage your computer." message is probably legal ass-covering, since any system that can't 100% CPU usage 24/7 is defective. Indeed, back when DOS was common, that's what it did to the CPUs of the time, as did other applications which used a polling loop instead of waiting for interrupts.