Sometimes referred to as the CPU, or central processing unit, the processor is the brains of the computer. It's the most important chip in a notebook, and it has power-management features that extend battery life. Laptops use a variety of processor types depending on their focus. We've explained each in the chart below:

Processor	Notebook type	Performance	Battery life	Price
AMD Athlon 64 for DTR	Desktop replacement
AMD Turion 64	All types
AMD Turion 64 X2 Dual Core	Thin-and-light
Intel Celeron M	Ultraportable, thin-and-light and mainstream
Intel Core 2 Duo	All types
Intel Core Duo	All types
Intel Core Solo	Ultraportable and thin-and-light
Intel Pentium M	Ultraportable, thin-and-light and mainstream
Mobile AMD Athlon 64	Mainstream and desktop replacement
Mobile AMD Sempron	Ultraportable, thin-and-light and mainstream
Mobile Intel Pentium 4	All types
Mobile Intel Pentium 4 with HT	All types

Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM (random-access memory). Computers store currently running applications and data in this area. To find out how much memory you'll need, take into account your operating system and the applications that you plan to use. A general rule of thumb: You'll want 512MB for Windows XP or Mac OS X and 256MB for all other Windows and Mac operating systems. If you hope to run Windows Vista when it's released in early 2007, you'll need at least 512MB, preferably 1GB.

If you're planning to hang on to your notebook for a long time, look for a laptop with easy-to-access memory slots, as memory is typically one of the first specs you'll want to upgrade.

Unlike traditional desktop CRT (cathode-ray tube) monitors, notebooks ship with thin, liquid-crystal displays (LCDs). Notebook LCDs range in size from 10.6 inches (diagonal) to 20 inches; display size is a key factor in the laptop's overall weight. For comfortable viewing at the preferred Windows resolution of 1,024x768, most people like 14.1-inch or larger LCDs.

The ultraportable Fujitsu LifeBook P1510 (left) has one of the smallest screens--just 8.9 inches--in order to accommodate its feather-light 1kg weight. The giant 17-inch Apple PowerBook (right), on the other hand, has the biggest notebook screen we've ever seen.

Notebook LCDs once varied widely in brightness, color, and sharpness, but today, you'll find much better quality across the board. Unfortunately, when it comes to LCDs, the specs reveal little about actual picture quality, so if you're picky about screens, compare some at your local dealer.

A notebook hard drive removed from the system.

This magnetic disk provides you with space to save programs and files indefinitely--or at least for the life of the drive. Notebook hard drives can provide up to 120GB of storage, but these giant drives cost hundreds of dollars more than the default 60GB to 80GB notebook drives. The 60GB to 80GB drive should be sufficient, unless you store lots of music and movies or tons of pictures. Be warned that capacity alone does not make a good hard drive. The hard disk's rotational speed also makes a big difference; a 7,200rpm notebook disk delivers significantly faster performance than a 5,400rpm model. The faster the disk spins, the better your notebook will perform overall.

Unless you're going budget, don't settle for anything less than a CD-RW drive.

Most notebooks, even budget systems, now include a CD-RW/DVD drive (either built in to the laptop or external and connected via USB) for burning discs and watching movies on the road. Some higher-end notebooks offer DVD burners, which let you store large amounts of information on one disc; double-layer DVD burners can pack even more data on a single disc. But unless you need to store huge files, such as movies, you may not need these more expensive DVD-RW drives.

Here is a media module slipping into a swappable drive. Fixed drives won't let you remove the module.

The least expensive notebooks come with fixed (built-in) drives. In other words, if you buy your notebook with a fixed DVD-ROM, you're stuck with that drive. A swappable drive bay, on the other hand, gives you optimum flexibility. For instance, you can pull out the DVD-ROM drive and swap in a combo DVD/CD-RW drive or even a second battery. We recommend going with a swappable bay if you can afford it. Keep in mind, however, that the smallest and lightest ultraportable notebooks may include neither fixed nor swappable optical drives, relying instead on external USB drives.

This is an external drive tethered to a Sony notebook.

External drives--storage and media-burning options that hook up to your notebook via cable--come in many shapes and sizes. Most of these drives connect to your notebook via a USB or FireWire cable. Drive choices include external floppy, CD-ROM, combo DVD/CD-RW, DVD-ROM, DVD-RW, hard drive, and others. There are also smaller external drives, called thumbdrives, that plug directly into your USB connector sans cable. These little drives are brilliant for transferring small amounts of data between notebooks or between notebooks and PCs, and they're much more convenient than burning data onto CD. Many notebook users don't need external drives, but there are scenarios that require them. For instance, if you buy a tiny ultraportable that lacks a built-in CD-ROM drive, make sure you get an external one so that you can load software.

The PC Card, a credit card-shaped device that plugs into a slot on your notebook, can provide a number of connection types--modems, USB connections (say, for your digital camcorder), and wireless WAN radios are all available in PC Card form. PC Cards are handy because they're easy to upgrade and because you can buy third-party PC Card solutions after you purchase your notebooks. However, most notebooks come with only one or two Type II PC Card slots, forcing you to limit the number of PC Cards you can add.

The Proxim Orinioco World PC Card (left) and the Netgear WAB 501 dual-band wireless adapter (right) are two examples of PC Card wireless adapters with antennae that extend beyond the edge of the notebook.

ExpressCards are the next generation of the PC Card. Smaller than existing PC Cards, ExpressCards promise data-transfer rates that are twice as fast, which means the cards can be used for high-bandwidth interfaces, such as Gigabit Ethernet ports and HDTV tuners. The standard is still relatively new, so there aren't many ExpressCard modules on the market today; however, most current laptops include an ExpressCard slot for future use. If you know you'll want to add some of these high-bandwidth functions to your laptop after you buy it, consider a system that supports the new standard.

Though the standard is being phased out, most notebooks still come with a 56Kbps-modem (RJ-11) connection, and virtually all include Ethernet (RJ-45) or even faster Gigabit Ethernet connections. Almost all notebooks also include built-in antennas for wireless networking (802.11, or Wi-Fi) so that you can access wireless hot spots. If you choose a notebook with networking built in, consult our wireless network buying guide to learn the difference between the networking standards that are currently on the market, including 802.11a, 802.11b, and 802.11g.

If your travels regularly take you beyond the reach of Wi-Fi hot spots, you may want to consider spending a little extra for a notebook with a built-in WWAN card. These systems let you tap in to a cellular provider's data network. They can be incredibly useful when connectivity is spotty, but the technology has its downsides: data plans still tend to be pricey; throughput speeds, while improving, are still slower than most high-speed Internet; and your built-in cellular card can work with only one cellular provider.

Depending on the model you choose, you may also have the option (often for an additional cost) of ordering a Bluetooth adapter in your laptop. This will let you connect your laptop to other Bluetooth-enabled devices (such as a printer, a cell phone, or a PDA) that are in close range.

If your notebook doesn't include any of the above network adapters, it's fairly easy to find PC Cards that get the job done.

Most notebooks have a VGA port for an external monitor, Ethernet and modem jacks, headphone and microphone jacks, and two to three (or more) USB ports for connecting an external keyboard and mouse, drives, digital cameras, and MP3 players. For home use, you may want any variety of A/V connections, such as S-Video, DVI, or S/PDIF output, and a FireWire port for capturing and editing digital video or hooking up an external storage drive.

IBM's port replicator works for many different ThinkPad notebooks.

A docking station contains a mixture of ports, slots, drive bays, and security features, and it usually attaches to the notebook from underneath. Docking stations come in a variety of shapes, ranging from the same size as your notebook, which is often referred to as a media slice, to much bigger--some stick out five inches past the back of your notebook. As the name implies, a docking station is where you park your notebook when you get back to the office, giving you easy access to your network, along with a bigger monitor, a regular keyboard, additional storage devices, and the convenience of leaving cables plugged in when you walk away from your desk. A port replicator, on the other hand, is a smaller, stripped-down version of a docking station that mainly features--as you might guess--ports, such as USB or S-Video. A port replicator can range from the size of a box of toothpaste to just shy of docking-station stature. When you're on the road, a port replicator is a convenient way to increase your connectivity.

A solid notebook carrying case is worth the extra money.

You're about to drop a couple grand or more on a laptop, and the last thing you want to do is spend even more money on a carrying case. So, you save a few bucks by going with the manufacturer's basic case. But basic bags often lack a padded shoulder strap or internal pockets. You'll be kicking yourself soon when your nine-pound load is cutting a groove into your shoulder and all of your accessories come tumbling out of your bag in a tangled mess. Dig into your wallet for a sturdy, comfortable carrying case, and your shoulder will thank you. Look for padded shoulder straps, reinforced corners, and specialized compartments designed to hold the AC adapter, the extra batteries, and so on.

The Compaq Evo N410c features two extra batteries.

If you do even a modest amount of traveling, we recommend getting the largest battery available for your model--or, if you're wary of the extra bulk that a larger battery entails, get a second battery. They range from S$200 to S$400, and they are well worth the money if you plan to regularly spend more than two to three hours away from a wall outlet. Next time you're trapped on the tarmac working away on your laptop and your primary battery is about to die, you'll be glad to have that second cell. If you rarely travel with your notebook, however, and your laptop is pretty much always plugged in, don't bother with a second battery.

This is an external drive hooked via a cable to a Sony notebook.

External drives--storage and media-burning options that hook up to your notebook via cable--can be a pain to carry around and hook up, plus they can be pricey. You're generally better off buying a notebook that has everything you need out of the box. Nevertheless, external drives are sometimes required. If, for instance, you buy an ultraportable that lacks a built-in CD-ROM drive, make sure you get an external drive so that you can load software. Types of external drives include CD-ROM, CD-RW, combo DVD/CD-RW, DVD-rewritable, hard drives, and more. No matter what notebook you buy, we strongly urge you to invest in a thumbdrive that plugs directly into your USB connector sans cable. These little drives are brilliant for transferring small amounts of data between notebooks or between notebooks and PCs, and they're much more convenient than burning data onto CD.

Wireless keyboard and mouse from IBM.

Working for hours with just a pointing stick or a touch pad can take a toll on your hand, wrist, and forearm. To save yourself some wear and tear, invest in a small travel mouse. These can cost little, they usually hook up via USB, and they're very easy to tote. The same advice applies to typing for hours on your notebook's keyboard. If you plant your notebook on your desk when you work, hook up a USB keyboard and relieve your wrists. If you prefer working without wires, get a wireless mouse and keyboard.