One is a dual core 3.6ghz with hyperthreading for 4 virtual threads. The other is a quad core 2.8ghz with no hyperthreading, so 4 real threads. The 3.6ghz dual core can turboboost itself up to 3.8ghz if I remember right, on single threaded tasks, while the quad core can turboboost itself up to 3.4ghz on single threaded tasks.
sorry i didn't understand about this because i don't know a lot about these things.
is it really a big difference between them ? (like in gaming ?)
Apple only wants you changing out ram in the iMac, but nothing's stopping you from changing out the hdd or odd. The cpu and gpu are technically replaceable as well, but will void your warranty. There's also probably a limited amount of cpus and gpus that actually work with osx.
and is the cpu and gpu hard to find ?? expensive ?
is it hard to replace them ?