This alternative Kindle, called the DX, is a super-size version of the popular Kindle 2, which arrived earlier this year. It sports a 9.7-inch screen, some 2.5 times as big as the surface area of the Kindle 2’s 6-inch display. It also sports a higher price tag — $489, versus $359 for its smaller sibling, which remains on the market.

Amazon’s Kindle DX

Like previous models, the Kindle DX allows you to shop for, and wirelessly download, any e-book in Amazon’s (AMZN) growing catalog — now about 275,000 titles. It uses the same easy-on-the-eyes screen technology as the smaller model but at a higher resolution. It still lacks color, and renders images only in gray scale. But the new DX adds a new capability: auto-rotation, which allows you to read in landscape mode.

This new, larger model isn’t primarily aimed at readers of standard books. It is targeted at three markets: textbooks, newspapers and other periodicals, and business documents in either Microsoft’s (MSFT) Word format or Adobe’s (ADBE) PDF format.

Unfortunately, I’ve been testing the Kindle DX and I didn’t like it nearly as much as the Kindle 2, which I own and enjoy using daily. While it performs its promised tasks adequately, I found that its size and weight made it awkward and tiring to hold for long periods of reading. It’s still fairly thin and light, but it’s 85% larger and heavier than the standard Kindle.

In addition, Amazon has degraded the user interface. To prevent the device from being even larger, the company had to remove the left-side page-turning buttons, confining all the controls to a vertical strip on the right. The keyboard at the bottom is also more vertically cramped.

If you’re left-handed, you have to spin the device around and rotate the screen to get buttons on the left, where they appear with their labels upside-down.

Similarly, if you choose to read in landscape mode, all the navigation controls, including the joystick for moving the cursor, will be awkwardly placed at either the top or bottom, far from where your hands are holding the device, and the keyboard essentially will be unusable.

In my view, the Kindle DX would have been a better product with on-screen touch controls that could instantly adapt to its size and orientation.

In reading standard books on the DX, I also encountered instances where the text on a page varied in shade from light gray to black.

I had mixed results with business documents. As with previous Kindles, you can either email personal documents to your device, for a fee, or drag them onto the Kindle via a cable, for free. But, unlike the smaller models, the new DX has PDF display capability built in, so it renders PDF files much more accurately than the older Kindles. That is a big improvement. It also allows you to view Excel and PowerPoint files if you save them in PDF format before sending them to your Kindle DX.

The Kindle DX, right, is a large-screen version of the popular Kindle e-reader, left.

I tried a variety of documents, and in many cases the results were great. The text was crisp, and the tables and graphics looked like they should. But I found that on some of these PDF documents, the text was too small to read. Yet, the Kindle lacks the ability to zoom in on PDF documents. You often can make the type larger by rotating to landscape mode, but this splits the PDFs into multiple pages, sometimes breaking them awkwardly.

Also, Amazon has raised its fees for converting and delivering business documents via email to all Kindles. The charge was formerly 10 cents a document. Now, it’s 15 cents per megabyte, which can add up if you load up your Kindle with lots of large documents. Most of my test documents, which were fairly small, cost over $1 each.

Newspapers looked about the same on the DX as they do on the smaller Kindles. Despite the larger screen, they don’t use traditional print or Web layouts, but a special Kindle layout that some users like a lot, but which I find annoying because it makes it harder to quickly scan multiple headlines.

The Kindle DX does have some nice touches. For the extra money, you not only get a larger screen, but also about twice the storage capacity. Also, because the screen is wider, you can adjust the margins on the DX, to obtain a line length that’s comfortable for your eyes and optimal for reading speed.

Amazon claims the same multiday battery life for the DX as for the Kindle 2. In my tests, I was able to go for several days of moderate reading without recharging, and much more if I turned off the wireless capability.

Although I wasn’t able to test college textbooks, I suspect they may be the killer app for this product. Many already are so expensive and heavy they could make the weight and price of the Kindle DX seem trivial in comparison.

But for standard books, I’d stick with the smaller, more comfortable Kindle 2.

Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com. Email him at mossberg@wsj.com.

The arrival of a large update like this isn’t a sign of trouble, or even unusual. Microsoft has routinely issued these large “service packs” periodically for Windows. And just this week, its competitor, Apple, unleashed an even larger update for its new operating system, Leopard.

Even though they can take a long time to download and install, such updates are generally a good thing for consumers. Microsoft will automatically deliver SP1, as the company calls it, through its normal updating mechanism, built into Windows. The update is free.

However, based on my tests of Vista SP1, I believe that for most average consumers, it will likely be a nonevent, and for others it will be disappointing. Many of its benefits are aimed at corporations and power users, or are under-the-hood fixes that are hard to discern. For mainstream users, it adds no significant, visible features to Vista, and changes little or nothing about the way the operating system looks and works.

Also, SP1 doesn’t resolve some of the most annoying flaws in Vista, including slow start-ups and reboots, and a security system that nags you too much and requires add-on anti-virus software. I guess these problems will either never be fixed fully or will have to wait for SP2.

While Vista SP1 does deliver some performance improvements in certain scenarios, it can actually temporarily degrade performance — including making reboots even slower — because of a quirk in the update process. This slowdown should go away in a few days, the company says.

On balance, the update is probably worth installing, especially since Microsoft will deliver it automatically. But I wouldn’t rush to grab it and I wouldn’t expect much from it. One note: you can’t install SP1 until you have installed a couple of other patches first. These will also be distributed automatically.

I installed Vista SP1 on two computers that had come with the original Vista preinstalled: a 10-month-old Sony Vaio SZ laptop and a two-month-old Dell XPS One desktop. Because the automatic download distribution isn’t yet in place, Microsoft sent me the update on a disk, which also included the prerequisite patches. In each case, the upgrade took a little over an hour and went smoothly. During the process, the computers rebooted multiple times, but it was all automatic and didn’t require user intervention.

After the installation, the computers functioned normally. I tested three of the performance improvements Microsoft claims for SP1. The first involved speeding up the copying of hefty folders containing large numbers of files. On both machines, copying a folder containing over 700 files totaling almost 700 megabytes took less than half as long with SP1 as it had with the original Vista.

I also tested how long it took both machines to awaken from a hibernation or sleep state and be ready for work. For these tests, I began with each machine running Microsoft Word, Microsoft Outlook and the Firefox Web browser, then I forced them into sleep and hibernation mode.

By my definition, “ready for work” means that Vista’s circular delay indicator has gone away, the software that loads at start-up has finished launching and the computer has fully reconnected to its wired or wireless network. On both of my test machines, SP1 improved the recovery time from sleep or hibernation, shaving one to 10 seconds from the procedures.

Microsoft doesn’t claim SP1 will improve the speed of cold starts and reboots under Vista, but I tested these anyway. To my horror, I found that SP1 actually made rebooting — already slower than on comparable Windows XP computers or Macintoshes — even slower.

Microsoft explained that this was due to the fact that installing SP1 erases certain data used by Vista to speed up program launching. It takes the system a few days to build this data back up, the company says. Until then, it says, overall performance, including reboots, can be slower under SP1 than under original Vista.

Microsoft provided me with a method that would rebuild this program-launching data more quickly, at least for the common programs I was using in my tests. Once I followed that method, rebooting time returned to its former state — still too slow for my taste, but at least not worse.

In briefing me on SP1, Microsoft made a big point of saying that great progress had been made in the past year in making Vista work properly with add-on devices, such as printers. I tried my 2003-vintage Hewlett-Packard printer, which hadn’t worked properly with the original Vista. It still didn’t work well with SP1.

So, Vista SP1 is a step forward, at least after a few days of use. But it’s not a big step.

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.