> When i run the mame -prescale x command beyond value 3 from command line it says > 'invalid command, reverting to 1'.
Yep. I just looked at the source code and the valid values for prescale are 1, 2, or 3.
I don't see the harm in allowing higher prescale values. I don't know why it's capped at 3. 1-8 seems completely reasonable to me. Maybe one of the MAME devs will comment on this thread and explain the reason for the cap.