Thank you. This post lead me to the following website, which could answer my question.
http://perldoc.perl.org/perlfaq8.html#Why-can't-I-get-the-output-of-a-command-with-system()%3f
system runs a command and returns exit status information (as a 16 bit value: the low 7 bits are the signal the process died from, if any, and the high 8 bits are the actual exit value).
The answer to my original question: 16 bits are needed instead of 8 bits because also the signal id which killed the process has to be stored.
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