Well we get asked this one at least once a day and for good reason. The terms concrete mixer and mortar mixer get " mixed" together so frequently. So in short a concrete mixer has a rotating drum that spins used for materials that contain aggrigate from 1/4" to 1/2" in diameter.
A mortar mixer is more like a big blender. It uses mixing paddles with a stationary drum to mix powders like mortar, sand, plaster and grout. Keep in mind that you NEVER want to attempt to mix concrete inside of a mortar mixer. In the event that one of the 1/4" or 1/2" stones get caught between the wall of the mortar mixer and one of the paddles it would rip the gearbox right out of the machine and probably damage the mixing paddles heavily.
To see the different look of the mixers click below:
For concrete mixers
For Mortar Mixers