[Microsoft Surface] SixSixSevenSeven:
Its a very blunt difference.

The Surface RT uses an ARM processor. The Surface Pro uses an x86 processor.

As a result of that the Surface RT uses Windows RT

which is not the same as Windows 8

. Windows RT only runs on ARM processors and will not run software from previous versions of windows. All of your existing windows software will no longer work on the RT. RT can only install software downloaded from microsoft app store OR there is a jailbreak on these very forums allowing you to download software specifically ported for windows RT. Note, it must be specifically ported and there is no way of taking a DVD of software you already own and converting it for windows RT, basically if its not a piece of open source software then there is a 0% chance of getting it on your RT, if it is open source software then *eventually* you might be able to have a port but right now there are hurdles we need to get over first. Windows RT does come preinstalled with microsoft office though (although some macro's and extra features are missing). Internet explorer is the only web browser on it right now but does work in both metro and desktop mode. Someone is working on chromium (googles open source version of google chrome) but that has alot of problems that need solving yet. There is an x86 emulator but its too slow to be used on anything but software from the 90's maybe.

Regular versions of windows (including windows 8) can only run on an x86 processor (such as almost anything made by intel or AMD). The Surface Pro does have this and comes pre installed with Windows 8 Pro accordingly. As a result all existing windows software that you may own will run on the Surface Pro. Downsides are that the battery life is significantly impacted (Toms hardware recorded over 7 hours on the RT but only 5 on the Pro), the weight is increased, fans are needed to cool the intel core i5 chip empowering the Pro so you have noise from them and it costs about twice as much as the RT. The pro also gets a fancy wacom stylus.

If your just web browsing and can live with only using the microsoft store and the limited pool of software available via the jailbreak (read in the relevant threads for more info) then go for the RT as its cheaper.

But if you do need full compatibility with previous windows software you own then RT will just annoy you, you'll have to splash out more cash sadly.

One other thing. The surface RT and the surface Pro are not the only windows tablets on the market. Windows RT tablet choice is a little limited (and out of the bunch then either the Surface RT or the Asus Vivotab RT are the best in my opinion) but there are plenty of full windows 8 tablets. Some of the other full windows 8 tablets use an intel atom processor instead of an intel core i3/i5/i7. The atom processor powered tablets often manage to ditch the fans featured in the core i series devices, boost the battery life to be competitive with ARM/WindowsRT devices, reduce weight inline with ARM tablets and most importantly reduces cost to be more inline with ARM devices. Infact thats the most annoying thing about current Windows RT on ARM devices, there is very little reason to buy them when in the same form factor, cost, weight and battery life you can have a tablet running full Windows 8 on the intel atom which is an x86 chip. Downside to the intel atom compared to the core i3/i5/i7 powered devices is processing power. They are not very powerful. The core i3/i5/i7 could possibly be used for some light 3d gaming but the atom will probably only cope with 2d games and not so much in the way of 3d (although that said, my friend plays minecraft on a previous gen lower clock speed intel atom quite happily and according to all benchmarks the intel atoms are more powerful than my current laptop which also copes with minecraft).