library(parallel)

cl = makeCluster(detectCores())

clusterSetRNGStream(cl)
clusterEvalQ(cl, library(MASS))

results = clusterApply(cl, rep(25, 4), 
  function(nstart) kmeans(Boston, 4, nstart=nstart)
  )

i = sapply(results, function(result) result$tot.withinss)
result = results[[which.min(i)]]

stopCluster(cl)

library(parallel)
cl = makeCluster(4, type='PSOCK')

res = parLapply(cl, 1:1000000, sqrt)
system.time({res = parLapply(cl, 1:1000000, sqrt)})

stopCluster(cl)

cl = makeCluster(4, type='FORK')

res = parLapply(cl, 1:1000000, sqrt)
system.time({res = parLapply(cl, 1:1000000, sqrt)})

stopCluster(cl)