Separating the Power of EREW and CREW PRAMs with Small Communication Width

Abstract

We prove that evaluating a Boolean decision tree of heighthrequiresΩ(h/(m+log*h)) time on any EREW PRAM with communication widthmand any number of processors. Since this function can be easily computed in timeO(h) on a CREW PRAM with communication width 1 using 2O(h)processors, this gives a separation between the two models whenever the EREW PRAM has communication widthm∈o(h).