I agree with Neil that this thread has drifted off-topic and am ready to give my DOS/WS problems a rest. As a final update FWIW, I find that adding /MAXCPU=1 to the PSD=ACPI.PSD line in config.sys makes no apparent difference to whether the DOS session crashes (it still does) or Reboot via Ctl+Alt+Del works (it still does). Thank you, people, for having a go at helping.