I know that DOS systems never go idle, they just loop polling the keyboard. Parallels does not detect the situation, at least not with my Caldera DR-DOS 7.03 setup. The VM hogs one core with almost 100% busy. I know that there must be ways to detect these loops. A good implementation is the DOS VM inside OS/2. Correctly tuned, an idle DOS prompt does not use any CPU resources. Another issue: keyboard capture. Why do I have to click in the window to have the keyboard activated. IIRC, this was not neccessary in Parallels 3. A small TSR that allows keyboard and mouse sharing in DOS would be a good idea.