User cpu time VS system cpu time

[cronfy]

Hello,

I want to understand difference between user CPU time and system CPU
time in system accounting.

When some process uses many system CPU, does it really mean that
process prouduces heavy load on server and takes up resources that
could be used by other tasks instead? Or it only means that this
process performs many waits for, say, I/O operations?

Thanks in advance!

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// cronfy