An all in one (like an iMac) has to sit on the desk, so it's called a desktop. A portable (not to be confused with a luggable) notebook can rest on your lap (unless it gets too hot!) so its generally called a laptop. A mainframe is probably called that because it sits in a framed metal housing that doesn't move (like an A-frame or a picture frame.. it just sits there..) A 'tower' type "desktop" however is frequently too ugly to dare to put 'desktop' driving many users to hide the unsightly beasts under the desk on the floor.. I suspect that for lack of a better word, towers were allowed to be grouped in with non-towers (horizontal desktop units). They are not however filling the same roles. The difference becomes more sharp when you compare and contrast towers with the so-called "mini-PCs". What would a more appropriate class type name be for a 'tower' type computer? Carpetweight Comfooter Floortop Footwarmer Scaremouse Subdesktop Toestubber _________ ?