How often do new Mac computers come out?

IPhone gets an upgrade every year and the iPods get upgraded every few years, how long do the macs take to get an upgrade?

Example: MacBook pro upgraded to MacBook Pro with retina display

Kind of like all desktop computers, yearly the hardware is still improving.

Usually Apple updates Mac's when new hardware gets released. Intel is releasing processors in Q2.So it could be possible that we will see new Macbook Pro's and Air's this summer.

Depends on how steeply the sales of old ones fall off, how much inventory is on hand or in the pipeline, how quickly the suppliers can gear up for new model production, what the competition is offering, what the ghost of Steve Jobs instructs.

Usually Annually or if tech jumps a little and gets a significant boost earlier or later.