There are several reasons for this, including the security problems in the dominant Windows platform from Microsoft; spillover from Apple’s blistering success with its iPod music players; the fact that Macs can now run Windows programs; and Apple’s highly successful chain of company-owned retail stores.

But another key factor has been the Mac operating system, called OS X, which came out in 2001. It has proved to be as powerful and versatile for mainstream consumers as Windows, yet easier to use and more secure. And Apple has upgraded OS X far more rapidly than Microsoft Inc. has upgraded Windows, bringing out major new releases roughly every 18 months, while Microsoft struggled for more than five years to produce the latest Windows iteration, Vista, which came out in January.

On Friday evening, Apple will release yet another new version of OS X, called Leopard, to replace the current version, known as Tiger. I’ve been testing Leopard, and while it is an evolutionary, not a revolutionary, release, I believe it builds on Apple’s quality advantage over Windows. In my view, Leopard is better and faster than Vista, with a set of new features that make Macs even easier to use.

Leopard will come preinstalled on all new Macs. It can also be purchased for $129 as an upgrade to existing Macs that, depending on configuration, can be as many as six years old. Unlike Vista, which is sold in four noncorporate upgrade versions ranging from a $100 stripped-down “basic” edition to a $259 deluxe “ultimate” edition, there’s only one version of Leopard. It includes all the features, from those aimed at novices to those aimed at power users.

For me, the marquee features in Leopard are a new function called Time Machine that automatically backs up your entire computer in the background; two new methods, called Cover Flow and Quick Look, for rapidly viewing the contents of files without opening any programs; and new techniques that allow you to access the files in, and to remotely control, other computers on your network or connected over the Internet with a few clicks and no technical expertise.

Plus, Apple’s free software for running Windows on a Mac, called Boot Camp, which was formerly an add-on users had to download and install, is now built right into the operating system. And, in my tests, the third-party Fusion program for running Windows and Mac programs simultaneously continued to work fine in Leopard.

I did notice a few drawbacks, but they were minor. The menu bar is now translucent, which can make it hard to see the items it contains if your desktop picture has dark areas at the top. The new folder icons are dull and flat and less attractive than Vista’s or their predecessors on the Mac. While Time Machine can perform backups over a network, the backup destination can only be a hard disk connected to a Mac running Leopard. And, on the Web, I ran into one site where the fonts on part of the page were illegible, a problem Apple says is known and rare and that I expect it will fix.

While Apple claims the new system includes more than 300 new features, there is nothing on the list that could be considered startling or a major breakthrough. Some of Leopard’s features are unique, but many others — such as backing up data and quickly viewing files — have been available on both Windows and the Mac via third-party programs or hard-to-find geeky methods buried in the operating systems. Leopard has made them easy to find and use.

When I upgraded my personal iMac desktop to Leopard, it took less than an hour, and after the process was complete, all my programs, including the Mac version of Microsoft Office, the Firefox Web browser and Adobe Reader, worked rapidly and fine. I was still able to run Windows XP via Fusion. And my previous installation of Boot Camp, which turns the iMac into a speedy, full-fledged Vista machine after a reboot, worked perfectly. All my Vista programs and files continued to function properly.

With Cover Flow, users get a visual preview of a computer’s files without having to open programs.

In fact, every piece of software and hardware I tried on two Leopard-equipped Macs — a loaned laptop from Apple and my own upgraded iMac — worked fine, exhibiting none of the compatibility problems that continue to plague Vista. My old Hewlett-Packard inkjet printer, for which Vista lacks the proper software, worked instantly in Leopard, even over the network. And, unlike with Vista, it was able to print on both sides of the page. I popped my old Verizon cellphone modem card into the test Leopard laptop and it worked, too, with no software installation or tweaking.

Leopard felt about as fast as Tiger, and it started up much faster than Vista in my tests. I compared a MacBook Pro laptop with Leopard preinstalled to a Sony Vaio laptop with Vista preinstalled. Even though I had cleared out all of the useless trial software Sony had placed on the Vaio, it still started up painfully slowly compared with the Leopard laptop.

It took the Vista machine nearly two minutes to perform a cold start and be ready to run, including connecting to my wireless network. The Leopard laptop was up, running and connected to the network in 38 seconds. In a test of restarting the two laptops after they had been running an email program, a Web browser and a word processor, the Sony with Vista took three minutes and 29 seconds, while the Apple running Leopard took one minute and five seconds.

Here’s a rundown of some of Leopard’s key features. Much more detailed information is available at apple.com/macosx.

File management: Apple’s Finder, the equivalent of Explorer in Windows, now offers two new ways to quickly see what your files contain. You can still view them as icons or lists. But you can also use Cover Flow, the same system Apple uses in iTunes and on the iPhone to display album covers for music. In Leopard, a large preview of each file you select appears above the list of files in a folder, and you can rapidly scroll through these icons. These previews are live, and their contents can be viewed without opening the program that is normally needed to display them.

Time Machine backs up files.

For instance, if the file is a video, you can just click on it, and it will play. If it’s a multipage PDF file, you can click on it, and arrows will appear allowing you to flip through the pages.

An even better and deeper look can be obtained using a feature called Quick Look. Just hit the space bar or click on a toolbar icon, and a preview of any selected file zooms out. You can even view multiple sheets in an Excel file via Quick Look without launching Excel.

Another quick new way to see your files is available in the Dock, the Mac’s equivalent of the Windows Task Bar. Here, any folder you place on the right side of the dock will display its contents, after a single click, either as a grid of icons displaying miniversions of the file or as a “fan,” or arc, of such icons. These special Dock folders are called “Stacks.” Leopard includes one by default that is the destination for everything you download from the Internet, so your desktop will no longer get cluttered with downloads,

Time Machine: This built-in feature will continuously back up all of the contents of your Mac to either an external hard drive directly connected to the computer, or to a hard disk connected to another Mac running Leopard that’s on your network. The initial backup, in my tests, took all night, but after that, the system updates the backups hourly and I didn’t notice any slowdown during the process.

To recover any file you deleted, you simply click on the Time Machine icon, and you are taken to a view that shows file folders — or your email or address book or photo collection — in a stack of windows that appear to go on infinitely. You click on an arrow and the stack of windows zooms until you arrive at the last view in which the missing file existed. Then, you click “restore,” and the file is recovered in your normal desktop view. You can also restore whole folders, groups of files, or even an entire hard disk.

Shared computers: In Leopard, any computer that has been set to be shared on your network shows up on the left side of every Finder window. Click on it, and you can access whatever folders have been shared on those machines. Depending on the remote computer’s security settings, you may first have to enter a user name and password. It’s the simplest method I’ve ever seen for accessing other computers on a network. And it works with Windows PCs as well as Macs. When I first turned on the Leopard laptop in my office, it immediately found a shared folder on my colleague’s old Dell running Windows XP. She hadn’t even remembered sharing the folder, which contained files from 2003.

You can copy or move files to and from these shared computers, or view their contents with Cover Flow and Quick Look, or open them in programs on your own computer.

If you are a member of Apple’s optional .Mac service, which costs $100 a year, you can use a feature called “Back to My Mac,” which can access your Macs from thousands of miles away over the Internet. However, this feature works only over certain kinds of routers (not all of them Apple’s) and, as my router didn’t qualify, I couldn’t test it.

Remote control: For any Mac in your shared-computers list for which you have permission, you can take over the screen by simply clicking on a button called “Share Screen.” You can also remotely control distant Macs over the Internet using Apple’s built-in iChat instant messaging program, as long as you have permission and the Macs are running Leopard.

Stacks displays the files in folders in the dock.

iChat: Apple now allows you to use its instant messaging program with Google Talk as well as AOL’s AIM service, and you can set up a video chat in which you can present a slide show or display a document. You can also add special backgrounds that can make it look as though you’re someplace else, like Paris. In my tests, this even worked with someone on the other end using a Windows XP computer running the latest version of AIM.

Spaces: In order to cut down desktop clutter, Leopard lets you set up as many as 16 different desktops that can run simultaneously, with different programs open in each. You switch among these desktops by using keyboard commands or a menu.

For instance, you might have your iPhoto and iTunes running in one “space,” or desktop, your Web browser and email program in another, and Windows XP in another.

Leopard isn’t a must-have for current Mac owners, but it adds a lot of value. For new Mac buyers, it makes switching even more attractive.

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.

The transdermal patch uses thousands of microneedles to inject drugs just below the skin without hitting pain receptors (a vast improvement over dot-matrix printer patches, which hit all of them at once). And it can be programmed to deliver specific dosages on a preselected schedule. It could, for example, monitor a patient’s cardiovascular system and adjust drug dosages to maintain a constant blood pressure. “The programmable part [of the patch] comes from HP’s inkjet technology, where we could program to fire different nozzles for ink, and we repurposed that for firing drugs,” Lim Eng Hann, associate director of HP’s Asia-Pacific IP Licensing Center, told ZDnet. Added John O’Dea, CEO of Crospon, a medical-device company in Ireland that will manufacture the patch: “We believe it’s an industry first to be able to deliver multiple drugs through a single patch with microneedles.”

The patch is at least a few years away from market. But when it finally arrives it may well revolutionize the drug-delivery arena–and perhaps even the market for OEM printer cartridges …

The transdermal patch uses thousands of microneedles to inject drugs just below the skin without hitting pain receptors (a vast improvement over dot-matrix printer patches, which hit all of them at once). And it can be programmed to deliver specific dosages on a preselected schedule. It could, for example, monitor a patient’s cardiovascular system and adjust drug dosages to maintain a constant blood pressure. “The programmable part [of the patch] comes from HP’s inkjet technology, where we could program to fire different nozzles for ink, and we repurposed that for firing drugs,” Lim Eng Hann, associate director of HP’s Asia-Pacific IP Licensing Center, told ZDnet. Added John O’Dea, CEO of Crospon, a medical-device company in Ireland that will manufacture the patch: “We believe it’s an industry first to be able to deliver multiple drugs through a single patch with microneedles.”

The patch is at least a few years away from market. But when it finally arrives it may well revolutionize the drug-delivery arena–and perhaps even the market for OEM printer cartridges …

Kodak’s main weapon in this new war is cheaper ink. Traditionally, H-P and other makers have sold the printers for relatively little, then made most or all of their money on the ink cartridges.

So, Kodak decided to reverse that business model. Its three new printers start at $149.99, not sub-$100 bargain prices. But its black ink cartridges cost just $9.99, and the color ones — which combine five color inks — just $14.99. And these are standard-capacity cartridges, not small or starter versions. Comparable H-P cartridges vary in price, but can easily cost double that, or more.

Kodak hopes consumers will be willing to spend more upfront for the printer to save later on the ink.

In a counter-move, H-P announced Tuesday that it will also be introducing new lower-price cartridges. But these new low-end cartridges will work only on future printers (and a few very recent models). And they will hold less ink than today’s standard. Plus, they will still cost more than Kodak’s cartridges: $14.99 for black and $17.99 for the combined color versions. H-P will also start selling larger-capacity “value” cartridges for the new printers that will cost about twice as much as the low-end ink, but print up to triple the number of pages.

How good are Kodak’s new printers? After all, cheaper ink isn’t really a bargain if the printer is lousy. To find out, I’ve been testing Kodak’s midrange model, the EasyShare 5300, which costs $199.99. It’s an “all-in-one” machine that combines a printer with a flatbed copier and scanner.

I compared this new Kodak with a roughly comparable all-in-one H-P model, the Photosmart C6180. This particular H-P model costs $100 more than the Kodak, because it includes some additional features. But H-P says that this printer has the same printing, scanning and copying quality and speeds, in the typical scenarios I tested, as H-P’s C5180, the direct competitor of the Kodak 5300, which costs the same.

My conclusion was that the Kodak EasyShare 5300 is a pretty good printer, with a good enough combination of quality, speed and functionality to satisfy people attracted by the lower ink costs. In my tests, it was better than the H-P at some things and worse at others.

One caveat: I didn’t try to verify Kodak’s claim that, overall, its printouts cost a lot less than H-P’s. Such claims depend on very specific sorts of test files produced and tested in labs. H-P disputes Kodak’s testing methodology and claims that Kodak’s printout costs are “about the same or only slightly lower than H-P’s.”

Also, the particular H-P models with which the Kodak printers most closely compare use a different ink system than most other H-P home inkjet printers. Instead of using one combined color cartridge that can cost over $30, they use five smaller separate ones that cost $9.99 each.

I decided to avoid settling this technical dispute and to just judge the printers using home photos and text pages from Microsoft Office that I considered typical. I used both printers at normal quality levels and didn’t enable any special quality or speed settings. I tested them with a Windows XP computer, though both printers also work with Macs and with the new Windows Vista.

In general, the H-P was a little faster, but not dramatically so. And the H-P has built-in networking, while the Kodak doesn’t. The H-P also has a better user interface, in my opinion. Kodak’s can be clumsy.

But the Kodak has a cool scanning feature the H-P lacks. You can place three or four photos on its glass plate at once and the printer will separate them automatically into individual images and scan them as separate files — as long as they aren’t aligned too crookedly. To do this on the H-P, you must manually draw lines around each photo with the H-P software.

When I compared plain-paper printouts, in black and white, and color, the printers were about equal in quality. The H-P was a tad faster, but the Kodak was plenty quick.

On photos, I had a mixed result. The 4×6 snapshots of family scenes came out better, to my eye, on the Kodak. They seemed sharper and brighter than the same files printed on the H-P. But I had just the opposite result when scanning several 20-year-old photos into the two machines. The resulting files produced by the H-P seemed sharper and brighter. The Kodak scans, while warmer, seemed fuzzier.

The worst feature of the Kodak is the way it switches between its plain-paper feed tray and its special separate tray for 4×6 snapshot-size photo paper. On the Kodak, you must manually push in and pull out the photo tray to switch between types of paper. The H-P handles this switch without any pushing or pulling.

Overall, however, the Kodak is a good enough first effort to get the company into the game.

• Email me at mossberg@wsj.com. See video versions of my reviews at wsj.com/mossbergvideo.