The single most important thing to consider when trying to decide which computer system will suit you, is exactly what you're going to want it to do. You need to stop and make sure you plan out exactly what it is likely to be used for over the course of the next couple of years that you own it.
If the sole purpose for you buying a computer is to do university assignments on, and you cant fathom ever possibly using it for anything else, then your requirements are going to be very different to those of someone who wants to also be able to play the latest shoot-em-up games.
Once you have worked out exactly what you are going to be using your new computer for, have a read through our detailed article on the information that will typically be available to you on each computer system once you are in store, and how to use this information to decide on the best system for your needs. It may be a bit of a read, but it's much better than making a critical mistake in your selection and being stuck with a computer that is insufficient for your purposes.
Now when you wander into the hardware section of your computer store, you will likely be faced with a scene something like this. Lots to choose from, and only a sheet of facts to distinguish one machine from the another. You usually wont get to see the guts of the system in the showroom, and even when you can, there's still only so much you can tell about a machine from looking at it.
For this reason, it is important to know, at least roughly, what the specification sheets tell you about a system, and what makes each thing important or irrelevant to you. The next page will discuss the specifications you will likely find presented here, and what they tell you about the machine they refer to.