mirror vs prism

ok so i was compareing some cameras on the canon website and i noticed something between the t2i my camera and the 7d which i pln on getting someday. the t2i has what they call a pentamirror viewfinder, if im saying that right and the 7d has a pentaprism. can anyone tell me what the diffrence is and how it benifits mirror vs prism.

http://www.thephotofor​um.com …mirror-vs-pentaprism.html

In a nutsell...

Pentamirror vs pentaprism is one thing that distinguishes the Rebel/xxxD/xxxxD from all the other models.

The pentamirror is a less expensive to produce design that's used in all the Rebel/xxxD/xxxxD series cameras....

The pentaprism is heavier and more expensive to produce, but gives a bit brighter and potentially larger image in the viewfinder. Canon uses pentaprisms in all the xxD and xD models.

ultimatly it is just for the vf nothing to do with the picture taking what so ever kind of a silly thing to worry about now that i know

Well, I can say that I appreciate the pentaprism on my Camera's... It's like looking through a full size window to see what's going on instead of a little thick glassed portal to view the world Live View, no difference, but I don't live view

A pentamirror is cheaper, lighter, smaller, and darker than a pentaprism, but in reality it should only be an issue if you will be manually focusing through the viewfinder (i.e. not live view) in less than bright light using slower lenses.