Checkdisk??

Hi,
I wanted to see how the checkdisk was working.
But he asked to plan it after restart because the disc was in use.
I said yes....and he started to perform it after restart.

Like the defragmentation it runs for a long time very long time.

But defragmentation one can stop....

My questions:
-if one has said yes...can it be cancelled and where?
-once it is started can it be stopped and it yes how?

Regards
Huib