Hi Skip,

I find different measurements om Windows/XP: I copied the script and ran
it under Python 2.5.2 and Python 2.6 (as downloaded from
http://python.org/ftp/python/2.6/python-2.6.msi):

Plappert@action-time /cygdrive/e/tmp $ python ./timing.py # 2.5.2
time with os.popen :  0.296999931335
time with subprocess.Popen :  0.203000068665

in other words: identical or subprocess.Popen even faster.

and it is getting even better with Python2.6:

Plappert@action-time /cygdrive/e/tmp $ python26 timing.py # 2.6
time with os.popen :  0.266000032425
time with subprocess.Popen :  0.18700003624

So could that be a Mac OS issue?