Hard Drive: A computer's hard drive stores all your programs and files. A drive with a higher storage capacity (measured in GB) lets you save more data than a drive with a lower storage capacity. You only need 20GB to 40GB of hard drive space if you only plan to store your operating system, programs, documents, and a few photos. You'll want at least 80GB if you plan to save a lot of large files such as high-resolution images, movies, or your entire music collection. Additional external hard drives also work well for data backup purposes and for storing large files.
Memory (RAM): Programs, including operating systems, need a certain amount of memory (RAM) to run, with more RAM providing better performance. For example, Windows XP requires at least 128MB RAM to run according to Microsoft. Most people find the number closer to 256MB and see even better performance with 512MB RAM, 1GB RAM, or more.
CD and DVD Drives: When you buy any computer you want a way to back up your work. Some laptops come with fixed internal drives while others have a hot-swap bay where you can insert and remove a CD drive, DVD drive, or combo drive. Combo drives can read or write to two media formats. They may also include a read-only media format such as CD-ROM (to read CDs) or DVD-ROM (to play DVD movies and read CD-RWs). With hot-swap bays you can always upgrade to a different drive (for example, from a CD burner to a DVD burner) later and you can sometimes use an extra battery with the bay.
Ports: Make sure you have the ability to connect all the peripherals and gadgets you want. Besides a parallel or USB port for your printer, you'll want USB 2.0 or FireWire to connect your MP3 player, digital camera, or camcorder. Many devices also work with USB 1.1.
Screens: While most folks will love a 14.1-inch display, some people may want to sacrifice size to drop some laptop weight. If you work with a lot of multimedia or play 3D games, go with a larger display.
Networking and Wi-Fi: If you want to connect to the Internet from more than one location in your home or office, find out if the laptop has built-in Ethernet support, a PCMCIA network interface card, or Wi-Fi (802.11b or 802.11g) support. For more information on wired and wireless networking, visit eBay's Networking Buying Guide.
Graphics Card: A graphics card processes video, freeing up memory (RAM) for other system tasks.