Hi I happen to use Xp and Vista 32-bit editions but have never come across a 16-bit OS. I really don't know what this __-bit thing actually means and would like to know. The only other place i came across this is under the display properties>settings tab. There is a drop box with options 16-bit and 32-bit (i know "this" 32-bit gives more colour.). So if I were using a 64-bit OS, then would I have an option with 64-bit colour too? Why are 64-bit OSes not very popular. And are 64-bit versions of Windows (XP & Vista) backwards compatible, ie. can regular software that runs on my system now also run on a 64-bit OS?