This reminds me of something that I have often wondered about. Unlike the datasteps above, PROC OPTEX reports in the log the random seed that has been used. I assume this is also derived in the same way from the internal clock. The random seed reported is nearly always a 9 digit integer that ends in either 001 or 000 (I am using SAS on a Windows 7 machine). Should I worry about this non-randomness of the last 3 digits? I suspect the number of digits from the clock is limited and a multiplication takes place to put the seed on a larger scale, but it would be interesting to know the mechanics of this.