Laptops and netbooks have them built in ( usually a pin hole near web cam ).
For someone to track you by use of your microphone they would have had to have infected you or had access to your system physically to add a listener service.
If you want to be sure your not being listened to then do a factory install or clean installation of the system. No need to destroy the built in microphone as for it can only be enabled if your system was compromised.
If its a desktop computer 99% of them dont have built in microphones but they have the jacks to attach them. If its an all in one desktop then it could be part of the 1% that actually do have built in microphone.
btw ... there are so many ways to track people without use of microphone. So if the computer is being used for anything shady on your behalf, the microphone alone wont save you from being tracked and I cant share details on what other ways you can be tracked because we cant assist those who are up to no good trying to hide etc.
