This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
The JDK and JRE downloads are different for different operating systems, eg Windows, Linux. And there may be different versions for different chips, but most people nowadays use an i386, which works on Pentium, most AMDs (I think, not sure), etc.
subject: difference between software portability and platform independence