Logarithmic Time Cost Optimal Parallel

When looking for new and faster parallel sorting algorithms for use in massively parallel systems it is tempting to investigate promising alternatives from the large body of research done on parallel sorting in the eld of theoretical computer science. Such \theoretical" algorithms are mainly described for the PRAM (Parallel Random Access Machine) model of computation 13, 26]. This paper shows how this kind of investigation can be done on a simple but versatile environment for programming and measuring of PRAM algorithms 18, 19]. The practical value of Cole's Parallel Merge Sort algorithm 10,11] have been investigated by comparing it with Batcher's bitonic sorting 5]. The O(logn) time consumption of Cole's algorithm implies that it must be faster than bitonic sorting which is O(log 2 n) time|if n is large enough. However , we have found that bitonic sorting is faster as long as n is less than 1:2 10 21 , i.e. more than 1 Giga Tera items!. Consequently, Cole's logarithmic time algorithm is not fast in practice .