Not perfect, but try multiple instances of

gzip < /dev/zero > /tmp/FILE

This won't hit IO so much though. dd is better for that, a variation of:

dd if=/dev/zero bs=8192 count=100000 of=/tmp/FILE

Execute the following commands 4 times

save the bellow commands under a file name then give execute permission to that file and execute it 4 times in background

the script creates 100000 factorials...

dc << EOF

[la1+dsa*pla1000000>y]sy

0sa1

lyx

quit

EOF

Thanks ! I'll maybe (carefully) try both at once !