The CPU is the heart of any computer, and is responsible for running the operating system and every application. A speedier CPU means faster-running programs, but usually it also means lower battery life and a more expensive laptop. Nearly every laptop has a CPU from either AMD or Intel.
If you're buying a netbook, you'll find that it uses either Intel's Atom line of CPUs, or AMD's Fusion E-series. The Atom line offers pretty slow performance and poor integrated graphics, but the battery life is phenominal. AMD's Fusion E-series chips are a bit faster, with dramatically better graphics and video decoding, but you'll sacrifice an hour or two of battery life for it. Neither choice is powerful enough for the most demaning tasks, like encoding HD video or playing the latest games.
Ultraportable PCs generally use low-voltage AMD or Intel processors. These chips are usually dual-core CPUs that are quite similar to the regular notebook CPUs found in larger laptops, but run at much lower clock speeds (1.2GHz instead of 2.1GHz, for example). Lots of processors--too many to list here--are available in this group. When you're shopping, however, you can follow a few general rules: More cache is preferable, and higher clock speeds are better but will drain the battery a little faster. AMD's CPUs are a bit slower than Intel's, but are priced to move and offer superior integrated graphics. Note, too, that some ultraportables don't use low-voltage CPUs, and are considerably faster (but have shorter battery life) than those that do.
All-purpose and desktop-replacement laptops offer both dual-core and quad-core CPUs in a range of speeds. Intel's Second-Generation Core CPUs (Core i3, Core i5, and some Core i7) are excellent for most users; only people who truly require a quad-core CPU (for encoding video, playing games, or running engineering applications, for example) would want a quad-core Core i7 processor. Again, more cache and higher clock speeds are better, but any CPU over 2.0GHz is fast enough to handle all the basic stuff, such as playing music, browsing sites and playing Web games, displaying online video, and managing e-mail.
You'll also find laptops with AMD processors. AMD's new Fusion A-series processors aim to offer better value in affordable all-purpose and ultraportable laptops. While the CPU part of these processors aren't as fast as Intel's, the graphics portion is far superior. What's more, the battery life stacks up well against Intel's processors. This wasn't the case with older AMD processors, which ate through your battery a couple hours faster than Intel's.
The graphics processing unit in a computer is useful for more than just playing games. This bit of silicon is ultimately responsible for everything you see on screen, from 3D games to the basic Windows desktop. Perhaps more important for some people, many GPUs can accelerate video decoding: With the latest version of Adobe Flash and the right GPU, Web videos from Hulu or YouTube will run more smoothly and look better (especially if you buy a netbook or an ultraportable laptop with a weaker CPU).
Most laptops are available with a choice between integrated graphics (from Intel or AMD) or a discrete GPU (from Nvidia or AMD). Integrated graphics are built into either the system chipset (the "traffic cop" that controls the flow of data in the system) or, in newer systems, the CPU itself. They share the main system memory with the CPU. Discrete GPUs are individual chips that are dedicated to graphics and have their own pool of memory, which results in far better performance.
Integrated GPUs from Intel are generally quite poor: They don't run 3D games very well. Second-generation Intel Core chips have dramatically improved video decoding, and the 3D graphics are faster, too. Still, they're too slow more most modern 3D games. AMD's integrated graphics is a significant step up, even capable of playing modern games at reduced resolution and detail. If you want to play games other than the occasional Web-based diversion, you probably want to select discrete graphics. You'll find lots of graphics chips to choose from, but in general the Radeon 6000 series from AMD is faster than the comparable 5000-series models, and the 500 series from Nvidia is speedier than the comparable 400 series. Within each series, the more-expensive models are swifter: ATI's Radeon HD 6850M is faster than the Radeon 6550M, and Nvidia's GeForce 560M is faster than the GeForce 520M, for example.
Memory is as important on a laptop as it is on a desktop. In fact, because laptop hard drives tend to be slower than their desktop counterparts, it may be more important. The more RAM a laptop has, the less often it needs to load data from the hard drive, after all. It's a good idea to get at least 4GB of RAM if it's offered as an option. Beyond that, the benefits are usually small and the cost to add more RAM is high.
Laptop memory these days is almost always DDR3, which is faster than the DDR2 memory commonly found in laptops as recently as a year ago. You'll also see a clock speed listed on some laptop memory specs, such as 800MHz, 1066MHz; or 1333MHz. The higher that number, the faster the RAM. Spend the money to get to 4GB first, and then worry about speed--if your choice is between 4GB of 1066MHz or 2GB of 1333MHz memory, go with the 4GB of slightly slower RAM: You'll get more performance bang for your buck by doing so.