The random seed is an initial integer used by our random number generator. Given a seed value, it provides a random number which ultimately determines the trajectory of the predictions. In other words, identical work units that use the same random number seed should provide identical results. However, since there can be numerical differences between different operating systems and architectures there can be differences in results even with the same random number seed.
Each time a rosetta run initializes, it may either generate a seed based on the time on your computer or use a seed that we provide. If the seed is based on the time on your computer, then different #random seed# values may occur when the run is stopped and restarted.
We use the random number generator ran3 from numerical recipes. I have heard that lower numbers using this method may produce non-random numbers but we avoid low numbers.