Dear all, I am running R-3.0 on Slackware64 Linux (Linux marto 2.6.38.4 #1 SMP Thu Apr 21 20:48:11 CDT 2011 x86_64 Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz GenuineIntel GNU/Linux) Here is a minimal example: library(parallel); fun <- function(fileName) { file.create(fileName); Sys.sleep(time=120); } mcmapply(fileName=c("mcm1", "mcm2"), FUN=fun, mc.cores=2); mclapply(X=c("mcl1", "mcl2"), FUN=fun, mc.cores=2); Just compare the time stamps of the mcm* and mcl* files. You will see that while the mcl* files have equal time stamps, i.e. they have been created simultaneously, the mcm files are created one after the other, with exactly 120 seconds of difference. This is what I see on my machine: bash-4.1$ ls -l mcm* -rw-r--r-- 1 marto users 0 May 11 14:25 mcm1 -rw-r--r-- 1 marto users 0 May 11 14:27 mcm2 bash-4.1$ ls -l mcl* -rw-r--r-- 1 marto users 0 May 11 14:29 mcl1 -rw-r--r-- 1 marto users 0 May 11 14:29 mcl2 Any ideas? Best regards, Martin