Pretty much the Core 2 Duo will have better performance then something like the Pentium 4 Prescott series of Cpu's. A Core 2 solo has much better performance than a Pentium 4, so whether you go single or dual core, I highly recommend the Core 2 over any other chip. The benefit of a second core will only be noticeable if you do a lot of multi-tasking, or if you use applications that are multi-threaded (designed to use multiple cores simultaneously). If you use Photo Shop, do a lot of video/audio encoding or plan to play modern games on your new laptop, the dual-core version is a good investment.