okay, well first things first, it confuses people to refer to hard drive space as memory cause usually people think of ram when you say that. Anyways, the biggest hard drive I found for a laptop is 160GB, but it costs like $355, so unless you have a lot of money to throw around, it's basically out of the question. An external hard drive is a regular sized hard drive (laptop ones are smaller, partly wh ythey are so much more expensive for the same data size) but in a case that holds it and converts all the plugs it uses to thingsa more easily used outside of computers. Anyways, you can get a large external drive for pretty cheap comparatively, for instance a 160GB external will run just over $100, and you'd have 240gb total compared to 160 anyways with not going for a new internal drive. Plus you have to reinstall windows and all the other things that came with your laptop to make the internal work, not to mention it won't be covered by your warranty. External's aren't as fast, though, so if you're using a program that takes up a lot of hard drive space, it may not run great. And finally external's need a usb or, preferrably, a firewire connection to plug into the laptop. I think that's about all there is to say