hello, i have some questions about MPI-I/O. 1) when i trying execute my program using MPI-I/O. why when iam execute with 1 proses, execute time more good than when iam execute with 2 proses. am i wrong? this is my source code. MPI_File_open (MPI_COMM_WORLD, file_akhir, MPI_MODE_CREATE | MPI_MODE_WRONLY, MPI_INFO_NULL, &hasil); int jumlah1 = (((block-1)*16)+pad); int jumlah = jumlah1 / size; MPI_File_set_view(hasil, rank * jumlah * sizeof(char),MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL); MPI_File_write (hasil, output, jumlah1, MPI_CHAR, MPI_STATUS_IGNORE); MPI_File_close(&hasil); 2) and after that i have compared that source using MPI - I/O and with sequential I/O, apparently, sequential i / o is better than the parallel i / o. how it could be happen? this is my sequential source. if (rank==0) { hasil = fopen (file_akhir, "wb"); int test = (((block-1)*16)+pad); fwrite (output, sizeof(char), test, hasil ); fclose (hasil); } thanks a lot for your attention