Answer to: Can I replace the CPU with a faster one?You could try an i7 on a 1156 socket, like the i7-870 (http://ark.intel.com/products/41315/Inte...-Core-i7-870-Processor-8M-Cache-2_93-GHz) But this CPU was originally only available in the 27" iMac. This processor also has a higher TDP of 95 watt. Your i5 uses max 73 Watt. Using the i7 in your 21.5" might be problematic concerning the heat dissipation. There are a lot of 45 W or lower i7 CPU's, but i think they are much slower then the i5 you have now. The other bunch of i7s is 82 W or higher, which may cause problems in your iMac. Even the 82 W i7-860S is slower than your i5. I think if you want a faster system...you need to buy a new iMac.
Answer to: Can I replace the CPU with a faster one?Hi Tom, That website (ark.intel.com) is indeed the correct site where this information can be found. But when i look at both links I see one of them using the 1156 socket(i5-680) and the other the 1155 (i7-3770s) socket.
Answer to: MBP Unibody too slow. How to replace the PRAM Battery?Some wikipedia info about PRAM or CMOS battery: It is a backup battery used by the logic board/motherboard to run the clock circuit and retain the configuration memory while the computer is turned off. As said above, a failing PRAM battery would not slow down your computer, but your clock would be incorrect and set to a date far back in history (1 jan 1970) every time you start it up. And no, the PRAM battery has nothing to do with RAM. Hope this info helps a little...
Answer to: Can I replace the CPU with a faster one?The i5-680 Processor uses an 'LGA 1156' socket. The i7-3770s uses an '1155' socket. So i am sorry, but no you can't replace your CPU with any i5 or i7 from 2011 and 2012 macs.