New but not noob question

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http://forum.xda-developers.com – Hey there! I have just bought an xperia arc s lt18i. I am not a noob or new in android so u can answer my doubts normally, I will understand u lol! I had a galaxy s sl and I think everything was quite different and easier. galaxy s (i9000) ROMS, firmwares, kernels, mods, etc weren't compatible with mine (i9003) and flashing them automatically bricks the phone. I have been reading a lot here and I still don't understand something... --Are xperia arc and xperia arc s firmwares, roms, kernels and mods compatible with each other? Because I was going to root my lt18i (currently on official ic (HowTos)