Windows 8 Release Preview is available as a Free Download
Microsoft Windows 8 Preview is ready to download and installing it only as simple as for Consumer Preview. You can start the installation directly from the web page, instead of having to download an ISO file and burn that to an optical disc. You can still burn an ISO if you want, and the installer can also create a boot able USB stick so you can download Release Preview once and install it on multiple machines.
As with Consumer Preview, how much of a previous Windows system you can keep when you install Release Preview depends on which version you’re upgrading from; upgrade from Windows 7 and you can keep programs, Windows settings, user accounts and files; upgrade from XP and you only get accounts and files.
Unlike Consumer Preview, you can’t upgrade from any of the previous Windows 8 preview releases; what you get is a clean installation with all your files moved into a WINDOWS.OLD folder where you can retrieve them.
If you can copy the files to an external drive it’s much faster to do a clean install (which took ten minutes to get to the personalisation screen on our test PCs) than an upgrade from Consumer Preview (which took 30 minutes on all our test PCs).
System Requirements for Windows 8 any machine must have 1 GB of RAM, 16 GB of hard disk space and 1 GHz processor should be able to handle Windows 8. The minimum RAM requirements are 2 GB in case you would like to install the 64-bit version of Windows 8.
You can find more on answers by visiting official Windows Microsoft website