Switch -MT<threads> - set the number of threads
<threads> parameter can take values from 0 to 16. It defines the recommended number of active threads for compression algorithm. If it is greater than 0, WinRAR will use the multithreaded version of compression algorithm providing higher speed on multiprocessor architectures. Real number of active threads can differ from the specified.
If <threads> is zero, WinRAR will use the single threaded compression algorithm.
Change of <threads> parameter slightly affects the compression ratio, so archives created with different -mt switches will not be exactly the same even if all other compression settings are equal.
If -mt switch is not specified, WinRAR will try to detect the number of available processors and select the optimal number of threads automatically.