1. Method 1: Replace a 3.0 GHz processor with a 2.1 GHz processor. (Adjust as appropriate!)

   Now no process can use more than 70% of the original cpu.

2. Method 2: Write a cpu-bound monitoring process that consumes 30% of the cpu and run it at real-time priority. This works for my system, but you will probably have to adjust the constants for yours:

   #! perl -slw
   use strict;
   
   our $N ||= 1.75e5;
   
   while( 1 ) {
       Win32::Sleep 1;
       1 for 1 .. $N;
       Win32::Sleep 1;
       1 for 1 .. $N;
       Win32::Sleep 1;
       1 for 1 .. $N;
   }
   [download]

Question: Why do you want to limit processes to no more that 70% CPU?