Router Internal ports vs Adding Switch

Is adding an unmanaged switch the same thing as additional ports built in on the router? Or would you need to add a managed switch? What about performance of a switch vs built-in ethernet ports? I was thinking that performance could be decreased b/c you just have just 1 pipeline of 1GIG to the entirety of all of the switch ports whereas the internal built in ethernet has perhaps a 1GIG pipeline to EACH port.