## Create a test datafile of ~ 4MB
perl -E"say 'x 'x10 for 1 .. 2e5" > junk.dat

## Then load it into an array of arrays using a while loop 
## and check the memory consumed using the Task Manager or TOP 
perl -E"$n=0;$a[$n++]=[split] while $_=<>; <STDIN>" junk.dat
## On my system the process has used 214.8 MB

## Now do the same thing using map
perl -E"@a=map[split],<>; <STDIN>" junk.dat
## On my system this process has used 345.1 MB.