See NotebookComputer.

Most notebooks sold today cannot legally be sold as "laptop" computers. Modern processors run hot, and the heatsink often connects to the underside of the device. OneLaptopPerChild's device will be one of the few true laptops sold in the last decade.

''My ThinkPad R51 has a big air vent + heat sink on the left side and never gets uncomfortably hot

http://mlb-s2-p.mlstatic.com/ibm-thinkpad-r51-4267-MLB4898876053_082013-F.jpg