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Smoke testing is a term used to describe the testing process for servers after patches are applied.
The process typically involves making sure servers are rebooted in the right order, making sure they have completely rebooted, restarting applications in the right order, and then testing to be certain everything is working properly when users return to work in the morning.
This typically takes 30 minutes per server, depending upon your environment.
PCs are not typically smoke tested, or if so, not all of them.