Most Xbox 360s seem to look alike but there are some subtle differences that set each of them apart. For example there are the differences in the consoles that are offered within each bundle, such as the Core, Arcade, Pro, and Elite. There are also unseen differences that lie within the console itself. Over time Microsoft has come out with new hardware that is more efficient than previous versions, so the more recent the Xbox 360 purchase means the newer the hardware within that Xbox 360 will be.
The easiest way to examine the difference between each type of Xbox 360 is to check the outside of your Xbox 360. If you purchased a bundle other than the Core bundle than you will notice that your Xbox has a hard drive, as well as a shiny silver cover to your optical drive. It is easy to determine if your Xbox 360 has its own hard drive because the hard drive is not internal. It is located to the side of your Xbox 360 and is easy to distinguish from the console itself. You will also notice that if your Xbox 360 does not have a shiny silver covering to its disc drive it means you either have a Arcade, Pro, or Elite console. This does not really make your disc drive any better than that of the Core version as all consoles use the same disc drive, it just looks cooler. Now the easiest difference between each type of Xbox 360 to spot is the difference between the Elite console and all others. The reason it is so easy is because the entire console is black!
Now these methods really only work if the Xbox 360 that you are looking at has not been upgraded since its initial purchase. I say this because just because a 360 has a hard drive does not make it a Arcade, Pro, or Elite version in the same way that having a shiny silver covering to your disc drive does not necessarily make it anything other than a Core version as well. What Microsoft has really done an excellent job of is allowing users to customize their own Xbox 360s to really make them their own. So if you really wanted to you could purchase a Core Xbox 360 version and upgrade it to have the same performance capabilities as well as look of the Elite version, but in the end you would be wasting your money as it would be cheaper to just purchase the Elite version in the first place.
The second notable difference between each type of Xbox 360 are the differences in the internal components or hardware. As time has gone on technology has improved and Microsoft has continuously upgraded its Xbox 360s with newer, more efficient technology. For example, if you have purchased an Xbox 360 anytime after October 23, 2008 then you probably did not know that you had in your possession a Jasper 360, which is an Xbox 360 with the new and improved Jasper chipset. This new chipset may not provide any noticeable difference in the performance of your Xbox 360, but in actuality it runs quieter and puts out less heat than previous chipset versions.
The biggest difference between each type of Xbox 360 can be found between the Core version and the Elite version. The Elite version was not available to consumers at the same time the Core version was. The Elite version comes with a large hard drive, the core does not come with a hard drive at all. The Elite version has a slick black gloss to it, the Core just has the simple white covering. The Elite version more than likely comes with the new Jasper chipset, as a majority of the Elite consoles came out after the release of the newer chipset. The core version came out way before the release of the Jasper chipset, so I believe it is safe to say that most of the Core versions out there do not have the newer chipset.
Although there is a difference between each type of Xbox 360 it does not mean that each Xbox 360 cannot become just as good performance wise as the other. If you purchase a Core version and decide later on that you want to upgrade it to similar specifications to that of the Elite version you can do it with relative ease.