Switch -RI<p>[:<s>] - set priority and sleep time
This switch regulates system load by WinRAR. Possible task priority <p> values are 0 - 15.
If <p> is 0, WinRAR uses the default task priority. <p> equal to 1 sets the lowest possible priority, 15 - the highest possible.
Sleep time <s> is a value from 0 to 1000 (milliseconds). This is a period of time that WinRAR gives back to the system after every read or write operation while compressing or extracting. Non-zero <s> may be useful if you need to reduce system load even more than can be achieved with <p> parameter.
execute WinRAR with default priority and 10 ms sleep time:
WinRAR a -ri0:10 backup *.*