We enter Q2 2004 with unprecedented mobile technology choices. In addition to ever-improving notebook computers and Tablet PCs, most business and IT workers use powerful, PC-connected cell phones and smart phones and have access to other highly mobile devices, such as personal data assistants (PDAs), BlackBerry devices, and the like. If anything, we're hitting a bit of an inflection point: Just because we can do something, doesn't mean we should. And as many busy travelers will tell you, bringing a bag full of devices on a trip often causes as many headaches as it solves.

Responding to this proliferation of mobile options, device makers are finally consolidating functionality. Today, for example, you can buy a smart phone that includes an integrated digital camera and, thanks to Secure Digital (SD) card expansion and a software media player, can double as an iPod-like digital music player. Add Global Positioning System (GPS) functionality--both the hardware and software parts--and you have an all-in-wonder device that does it all. You can even grab an external keyboard for many models and use it to take notes in Pocket Word (Pocket PC) or a Word-like application (Palm OS).

But, as I've always noted, mobile devices are a study in compromise, because of size, capabilities, and most damningly, battery life. Although most people would probably be well-served by the limited version of Microsoft Word that ships with most Pocket PCs and Windows-powered smart phones, most people aren't the types of business travelers that would even own such a device, and those people need something a little more powerful for their word processing needs. So they bring a laptop, further burdening them on the road.

I've been a regular business traveler for almost a decade, and I've struggled with the proliferation of devices during that time, each promising to solve all my problems. When handheld PCs--the clamshell-like devices that predated Pocket PCs--appeared, I wondered whether such a machine, with its lightweight and excellent battery life, could replace a laptop on the road. For me, they couldn't: As noted earlier, the Pocket Word version included with the devices was too limited, the memory capacity was too small to handle my email, and the connectivity options were almost nonexistent. Today's Pocket PC devices are more powerful and far more connected, but their small screens make them inefficient for desktop-type work: a classic technological catch-22.

I need a full-featured Windows XP laptop, in the smallest possible form factor. I've always jealously watched my contemporaries from the Far East type away on tiny laptops that aren't sold here in the United States, not that it would matter--my large hands would render such a device useless. I've reviewed several subnotebooks over the years, and in 2003, the IBM ThinkPad X30 series was, perhaps, the ultimate travel companion. Small, light, and powerful, the X31 could be configured at less than 4 pounds, yet had a full-sized keyboard and killer battery life. It didn't seem that IBM--or any other company--could make such a device any smaller and still have it serve the US market.

I was wrong, of course. At COMDEX 2003 in Las Vegas, Nevada, last November, IBM gave me a preview of its ThinkPad X40 series, which finally debuted in February. The ThinkPad X40 series is even smaller than the X30 series, thanks to a unique edge-to-edge keyboard design, and it gets even better battery life than the earlier devices. The style is classic IBM: sleek, black, and high quality. Intrigued, I scheduled a review and eagerly anticipated its arrival. Personally, the timing was good: I need to purchase a personal-use notebook, and I want something small, fast, and light. Maybe, I thought, the X40 would be it.

Naturally, mobility comes at a price: At less than 3 pounds in its base configuration, the X40 can't use the powerful Pentium M 1.4GHz to 1.7GHz processor found in its X30 brethren. Instead, it uses an Ultra Low Voltage (ULV) Pentium M running at 1.0 or 1.2GHz. Because 1.7GHz Pentium M chips outperform all but the fastest Pentium 4 chips, I was hopeful that the ULV chips would be adequate performers--and for most people, they are: For business applications like Word and Excel, the tiny X40 performs admirably.

If you need to use performance-oriented applications, however, the ULV Pentium M comes up short. I found the system inadequate for Adobe Photoshop work or running Virtual PC virtual machines, even with a healthy dose of RAM. I don't see this shortcoming as much of a problem--a machine this small is clearly designed for mobility over performance--but it's something to keep in mind.

Aside from that performance concern, the X40 has proven to be a near-perfect device. Like virtually all subnotebooks, it features a 12" XGA 1024 x 768 pixel screen, which I consider the minimum useful resolution for running XP. It ships with at least 256MB of RAM, though my unit included a more palatable 512MB of RAM. The unit has a 40GB hard disk (fantastic for a machine of this size) and includes gigabit and wireless networking, optional Bluetooth technology, and a handy integrated SD card slot. (The X30 features a less-useful CompactFlash slot).

Like the X30, the X40 benefits from a removable media slice--a slab you can dock to the bottom of the unit--that adds optical disk expansion. My unit includes a CD-RW/DVD combination drive, but you can choose from a wide range of drives, from a simple CD-ROM drive to DVD burner. You can also choose between regular-capacity and high-capacity batteries, the latter of which provides a whopping 10 hours of juice. If battery life and size are your primary concerns, you simply can't do better than the X40.

The X40's keyboard, although a bit smaller than that of the X30, is still adequate and of the expected IBM quality. Again, I have pretty big hands, so getting used to the new keyboard took a while, but I was soon typing away, with only a minimum of mistakes. However, after a few hours of work, fatigue kicked in, and it's pretty clear that, for me, the X40's keyboard is smaller than the minimum size my hands require.

For most people, however, keyboard size won't be a concern, and I was struck again and again by the stunning battery life this machine provides. Like all mobile devices before it, the X40 is a study in compromise, but it's a compromise most business travelers will likely make quite happily. Configurable from $1400 to about $2500, the IBM ThinkPad X40 has raised my expectations about what a notebook computer can be. I highly recommend it.

Incidentally, you might be wondering what I've decided to do about a notebook. For my home office, I prefer a large, desktop-like notebook such as Dell's stunning Latitude D800 model, but for the road, I need something small and fast, with fantastic battery life. Not coincidentally, IBM will continue selling the ThinkPad X30 because it addresses a slightly different need than the recently introduced X40. Unless something dramatic happens in the next 30 days, the X30 will likely be my next notebook.