parallelization [closed]

dd if=/dev/zero of=/dev/null bs=2048k count=100000
dd if=/dev/zero of=/dev/null bs=2048k count=100000
dd if=/dev/zero of=/dev/null bs=2048k count=100000
dd if=/dev/zero of=/dev/null bs=2048k count=100000
dd if=/dev/zero of=/dev/null bs=2048k count=100000
dd if=/dev/zero of=/dev/null bs=2048k count=100000

209715200000 bytes (210 GB) copied, 4.2765 seconds, 49.0 GB/s
209715200000 bytes (210 GB) copied, 4.30042 seconds, 48.8 GB/s
209715200000 bytes (210 GB) copied, 4.31607 seconds, 48.6 GB/s
209715200000 bytes (210 GB) copied, 4.29339 seconds, 48.8 GB/s
209715200000 bytes (210 GB) copied, 4.29755 seconds, 48.8 GB/s
209715200000 bytes (210 GB) copied, 4.29938 seconds, 48.8 GB/s

real    0m25.791s
user    0m0.153s
sys     0m25.625s

why do these execute sequentially?

after running them in background -

209715200000 bytes (210 GB) copied, 75.8795 seconds, 2.8 GB/s
209715200000 bytes (210 GB) copied, 75.946 seconds, 2.8 GB/s
209715200000 bytes (210 GB) copied, 76.5718 seconds, 2.7 GB/s
209715200000 bytes (210 GB) copied, 81.5599 seconds, 2.6 GB/s
209715200000 bytes (210 GB) copied, 83.3975 seconds, 2.5 GB/s
209715200000 bytes (210 GB) copied, 83.4965 seconds, 2.5 GB/s

interesting. thanks for the help.

Because you are running them in the foreground - need to put an & at the end of each dd line to background them eg

dd if=/dev/zero of=/dev/null bs=2048k count=100000 & 
dd if=/dev/zero of=/dev/null bs=2048k count=100000 & 
dd if=/dev/zero of=/dev/null bs=2048k count=100000 & 
dd if=/dev/zero of=/dev/null bs=2048k count=100000 & 
dd if=/dev/zero of=/dev/null bs=2048k count=100000 & 
dd if=/dev/zero of=/dev/null bs=2048k count=100000 & 

Alex