What are CPU and non-CPU lenses?

Answer 1

Just to add a bit of information to OMG's answer...

CPU lenses are identified by the presence of CPU contacts. These are a row of small brass-colored bumps on the lens mount. Go to this page and click on "Enlarge Image," which is printed right below the picture of the lens.

http://www.nikonusa.com/template.php?cat=1&grp=5&productNr=2159#

Look at the row of 10 little things that look like tiny ball bearings all the way on the right hand end of the image. These are the CPU contacts.

Here's another example where they are easier to see.

http://www.nikonusa.com/template.php?cat=1&grp=5&productNr=2148#

This also points out that there are different numbers of CPU contacts on different lenses, as there are only 5 on this lens.

Answer 2

CPU lenses have a microchip inside the lens. These are usually lenses used on Auto focus cameras. Thus a Non CPU lenses have no microchip inside the lens. These are usually the lenses used on manual cameras.

Answer 3

CPU lenses have a built-in chip. Newer cameras bodies communicate with this chip for the lens details and aperture setting. Without this chip, you can forget about exposure metering with most cameras.
(When I hear about this topic, it's mostly about old, manual focus Nikon lenses.)

Answer 4

CPU lenses has the ability to auto focus.
Non-CPU focusing are done manually.