Switch -MT<threads> - set the number of threads
<threads> parameter can take values from 1 to 32. It defines the recommended maximum number of active threads for compression algorithm also as for other WinRAR modules, which can start several threads. While WinRAR attempts to follow this recommendation, sometimes the real number of active threads can exceed the specified value.
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.