I can buy a desktop with an I3 processor and 6GB of RAM for a really good price, but can I buy an I5 processor and plug it in? Are the motherboards set up for supporting only one processor? I do not want to go the I7 route yet, so can I just swap out the I3 with an I5?
Hardware speaking, both i3 and i5 are on socket 1156. However if you want integrated graphics, you will need an h55 board, and for all intents and purposes that eliminates the i5 7xx and i7 8xx. That confines you to i3 5xx and i5 6xx. Considering the i5 6xx are pretty overpriced, id stick with the i3 and 6 gigs of ram. Better yet, build your own!