Patrick and Keith, You both make very helpful points. Yes, I am from the Church of One-sided, but only because I've got hundreds of papers showing that one-sided implementations scale very well for my application and zero papers showing scaling for two-sided. You argue against one-sided using the prevalence of MPI-1 use, but if you look at my field, the exact same argument goes against MPI-1. The reason I am trying to participate in the MPI-3 discussion is because whenever you all finish the standard and the various implementations, I am the one who has to develop applications with it. I don't know all the low-level issues, but what I want is something that quacks like ARMCI. If MPI-3 RMA doesn't do that, I will continue not to use MPI. The reason I wanted MPI-3 RMA to take over for ARMCI is that vendors port and tune MPI first and I don't like having to wait a year to run NWChem, etc. on the leadership-class hardware. I don't care what happens under the hood (active-messages versus RDMA, etc.) as long as I can Put, Get and Accumulate without interrupting the remote processor. Why do almost everyone use MPI-1? Find me a syllabus for course on parallel computing which teaches one-sided anything. Find me on that doesn't teach MPI-1 exclusively. Yes, there will be a few out Berkeley for UPC, UIUC for Charm++, etc. but the overwhelming majority of parallel programming education today focuses exclusively on MPI-1. If you teach a man to fish, he will fish, not farm wheat. I often confuse RDMA and one-sided, among other things. I am a HPC code developer not a hardware designer or NIC-protocol writer. I'd love it if someone can tell me the (accessible) book I can read to figure these things out. I'm willing to plead ignorance on some of the low-level issues here if, in return, try not to claim that everything in my field can easily be done with MPI-1, since 20 years of papers say it can't (at least easily). All I'm trying to say telling me I should be using MPI-1 instead is not an argument. Jeff -- Jeff Hammond The University of Chicago http://home.uchicago.edu/~jhammond/