So, last year, when Samsung introduced a new class of tiny Windows computer called the Ultra-Mobile PC, I gave it a harsh review and advised waiting for an improved model. That first effort, the Q1, was spurned by consumers, despite the high hopes of Microsoft and Intel, which conceived the UMPC.

But Samsung now has come up with a much better version, called the Q1 Ultra, which will go on sale at major electronics stores starting next month.

I’ve been testing the Q1 Ultra and, at least for certain classes of users, I believe it’s a pretty good product, despite some lingering downsides and compromises. It addresses the biggest weaknesses of its predecessor and throws in other improvements, yet starts at a significantly lower price — $799 compared with $1,099 for the original Q1.

The biggest improvement: Even though the Ultra is a tablet computer, still able to accept handwritten notes and meant to be controlled by a stylus, this new model now has a built-in keyboard. It’s just a tiny BlackBerry-style keyboard but it makes writing emails and typing in Web addresses practical.

The Samsung UMPC still isn’t a mainstream product, or one that I’d recommend for most average users. It does run the full version of Windows Vista or Windows XP, but it’s still too compromised to replace a small laptop for most folks.

However, I do see the Q1 Ultra as a decent choice for people willing to put up with some limitations in return for the ability to carry a real Windows computer that is as small as a thin hardcover book and weighs almost nothing. These users include students and frequent business travelers who mainly want to take notes, write emails, do instant messaging and Web surfing, and play music and videos. For people who want to do a lot of word processing, or to create spreadsheets or presentations, it would be better to stick to a small laptop.

The Q1 Ultra is a sleek, shiny, black tablet with a bright, sharp seven-inch screen that feels great in the hand and has a built-in stand on the back so it can be used upright. It weighs about 1.5 pounds, is less than nine inches long and five inches wide, and is under an inch thick. It’s slightly smaller and lighter than last year’s model.

The Q1 Ultra is run by a special, low-horsepower Intel processor and has only one gigabyte of memory, which can’t be expanded. But it runs Vista acceptably, if not exactly speedily. You can get one with Windows XP for faster performance.

Samsung’s Q1 Ultra

The main flaws in the first model were a high price, the lack of a keyboard, a screen that had too little resolution to manage Windows, weak battery life, no built-in mouse buttons and no built-in cellphone modem to augment its built-in Wi-Fi wireless networking.

In the new Ultra model, the built-in keyboard, meant for thumb typing, is split, with half of the keys on either side of the screen. This approach looks daunting, but works pretty well once you get the hang of it. Unfortunately, Samsung and Microsoft didn’t build any intelligence into this keyboard, so it doesn’t automatically complete words, add punctuation and capitalize the first letters of sentences, unlike the keyboards on most smart phones.

While still the same size, the screen is both brighter and has a higher resolution, so open windows can be easily moved and closed. There are now mouse buttons and an optional internal high-speed cellphone modem is available. The navigation pad is simpler and is easily programmable, though you have to manually set its arrow keys to mimic the arrows on a real keyboard.

Alas, the battery-life problems remain. In my tests, where I turn off all power-saving software, use maximum screen brightness, turn on the Wi-Fi and play an endless loop of music, the standard battery lasted just two hours and five minutes, which translates to about three hours in more normal usage. The $99 optional extra-large battery, which adds a little bulk and weight, did only about 50% better.

And this little computer can still be pricey. The base model is $799, but there are three better-equipped models that can range up to $1,499. That’s almost as much as a tiny Fujitsu tablet with a regular keyboard, and way above Microsoft’s $500 target price for the UMPC.

Another big problem is start-up time. Even with no programs running, it took me over four minutes to reboot the Q1 Ultra and over two minutes to boot it after a complete shutdown. To speed up start times, Samsung suggests either turning off Vista’s snazzy graphics or ordering the one model with Windows XP, which costs $1,149.

Still, if you don’t do a lot of document creation, and value small size and weight enough to put up with some hassles, the UMPC finally is an acceptable choice.

• Email me at mossberg@wsj.com. Find all my columns and videos online free at the new All Things Digital Web site, http://walt.allthingsd.com.

All of this makes carrying a large laptop less and less practical. But the smallest, lightest models have historically included design compromises that have ruled them out for many users.

Lately, however, the computer industry has been beefing up the capabilities of the so-called ultralight models. They cover all the key bases for mainstream travelers. And you can actually use them in coach.

I’ve been testing two good examples of this new class of full-featured ultralight laptops, the Sony Vaio T250 and the Fujitsu LifeBook P7010. I like both machines, but there are some key differences between them.

The Fujitsu costs less, at $1,999 after rebate, yet it boasts more and better features, including a larger hard disk and more ports and connectors. But the Sony, which costs $2,199 after rebate, wins this comparison in three areas that matter greatly to travelers: It’s a bit lighter, a bit thinner, and it has much better battery life.

The Fujitsu LifeBook, top, and the Sony Vaio

And the Sony’s screen, while the same size as the Fujitsu’s, doesn’t extend upward as far when fully opened, making the Sony a bit easier to use when you’re seated behind a serial recliner.

Both laptops weigh only about three pounds and have very small footprints that fit easily on a coach-seat tray table. But, unlike past generations of light laptops, these two models include internal disk drives that can play, and record, both DVDs and CDs. So you can install software from a CD or watch a DVD on the plane.

The two laptops use the same Intel processor, a power-saving Pentium M running at 1.2 Gigahertz. That’s plenty of processor for common tasks. And both have built-in Wi-Fi wireless networking.

Each has a decent 512 megabytes of memory, though, in both cases, up to 64 megabytes of that memory can be siphoned off by the identical Intel graphics chips they use. The Fujitsu’s hard disk holds 80 gigabytes, the Sony’s 60 gigabytes.

Both laptops have wide-angle screens that measure 10.6 inches diagonally. That’s very small by today’s standards. But size isn’t everything. A high screen resolution can squeeze lots of material onto a small display, and both the Fujitsu and Sony sport a resolution of 1,280 by 768, which does the trick.

Also, both of the screens are of the new, reflective type that delivers great contrast, though that can be a problem if there’s a strong light source over your shoulder.

Because of their small size, both models have slightly cramped keyboards. But I found both quite usable. I liked the feel of the Fujitsu’s keyboard slightly better than the feel of the Sony’s, though the Sony has larger right-hand Backspace, Enter and Shift keys.

Another limitation common in past generations of little laptops has been battery life. To keep weight and size down, manufacturers have often scrimped on battery size. But these two models boast battery life that would allow for nearly constant work on a cross-country flight.

I put both machines through my tough battery test, where I turn up the screen brightness all the way, disable all battery-saving controls, and play an endless loop of music to keep the power-hungry hard disk spinning. The Fujitsu’s battery lasted a very respectable three hours and 38 minutes, meaning that in a more normal usage pattern, with battery-saving controls turned on, it would likely approach five hours of life on a single charge.

But the Sony’s battery life was truly amazing for such a small machine. In my test, it lasted four hours and 25 minutes, or 22% longer than the Fujitsu. In more normal use, with battery-saving controls enabled, the little Sony could likely approach six hours of life.

The Fujitsu weighs 3.3 pounds and is 1.26 inches thick, 10.27 inches wide and 7.83 inches deep. The Sony weighs 3.04 pounds and is one inch thick, 10.7 inches wide and 8.1 inches deep — mainly because its battery protrudes from the back a bit.

Both laptops have two USB 2.0 ports; a PC card slot; and a Firewire port (also called “1394″ or “iLink”). And each has a standard video-out port for use with desktop monitors, and a touchpad for controlling the cursor.

But the Fujitsu also has a built-in fingerprint reader, which can lock out anyone but people whose fingerprints it recognizes. And it has an S-video port, for hooking up to a TV, and a multiplicity of slots for camera memory cards. It can handle the popular Secure Digital and Compact Flash types of cards, as well as the Memory Stick Pro cards that are mainly used by Sony cameras.

In Sony’s typical proprietary fashion, the T250 can handle only Sony’s own Memory Stick Pro cards. And the Sony lacks S-video and a fingerprint reader.

If the extra features and lower price matter a lot, go with the Fujitsu. But if lower weight, thinner size and better battery life are your key considerations, the Sony is the better choice.

Write to Walter S. Mossberg at mossberg@wsj.com