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.

Such Web-based software has existed for years, but it was clumsy, slow and simplistic — no match for locally installed software. Common techniques, such as dragging items around the screen, were impossible. Seeing the results of an action often required the Web page to reload.

Now, developers are churning out Web-based applications that are so fast, rich and smooth they can hardly be distinguished from standard programs. And because they live online, these Web applications can be constantly updated; can run on both Windows and Mac computers; and can be easily integrated with other Web sites and services.

One of the best examples of these slick new Web-based application is Picnik, a sophisticated, photo-editing application offered free of charge at picnik.com. I have been testing Picnik and I like it a lot. It’s a fast and impressive program for tweaking and improving your photos, then posting them to popular photo Web sites, saving them to your own computer, emailing them, or even printing them.

Picnik, which comes from a small Seattle company called Bitnik, isn’t meant to compete with Adobe Photoshop, or to serve professional photographers or dedicated hobbyists. Instead, it’s for the same casual photographer who would use the limited editing tools in Apple’s iPhoto or Microsoft’s Windows Vista Photo Gallery.

Picnik isn’t a place to store your pictures, or a way to organize them — yet. The company says it will consider adding these features down the road. For now, it is focused on being an editing complement to popular Web services — such as Yahoo’s Flickr, Google’s Picasa Web Albums, and the independent Facebook — that already allow for storing and organizing photos. You could also easily use it as the main editor for photos you store on your hard disk.

The program is currently in beta, or test, phase, though in my tests it worked smoothly and surely. During this beta period, all of its features are offered for free. Later this summer, the company expects to end the beta period and begin charging something like $20 or $25 a year for access to some of the more rarified special effects that Picnik offers, though the core editing and sharing functions, and some of the effects, will remain free.

In my view, Picnik has a beautiful and responsive user interface that worked perfectly on the multiple Windows and Macintosh computers I used to test it. It worked equally well in the latest versions of the three best-known Web browsers: Microsoft’s Windows-only Internet Explorer, Mozilla’s Firefox (on both Windows and Mac) and Apple’s Safari (on both Mac and Windows.)

Picnik uses a simple tabbed interface across the top to navigate among its major functions. Edits and changes are previewed in real time, instantly, without the need for a page refresh or reload. Actions are confirmed with translucent messages that pop up on the screen and fade gracefully.

Any edit or special effect can be undone or redone instantly, all the way back to the original version of the picture, which Picnik retains on its servers during the editing process.

For example, you can zoom in or zoom out on a picture with a slider that works just as it would in a local program — the effect is immediate, with no jerkiness. If you wish to crop a picture, a pane representing the region to be included in the crop is superimposed on the photo. Everything inside the pane is sharp and clear, and everything else is faded a bit. This pane can be dragged, or resized, in real time.

Another example: If you want to tint a picture, the program shows you a color palette with a white dot you can move around the palette to pick your tint. As you do this, or move a slider that controls the intensity of the tint, the changes are instantly previewed in the picture.

None of this is unusual for a standard photo program installed on your computer, but it is impressive to see these effects happen so quickly and interactively in a program functioning over an Internet connection.

Picnik’s makers have struck partnerships with Flickr, Picasa and Facebook, and you can easily fetch pictures from these sites and post new pictures or edited versions of the originals back to the sites. You don’t need to switch to the sites themselves, they appear inside the Picnik Web page.

You can also upload pictures for editing from any other Web site, or from your hard disk, and you can email pictures to friends or to a wide variety of other sites, such as PhotoBucket, SmugMug and Snapfish.

The designers of Picnik have done such an elegant job that I wish the site would allow storage of photos, or organization of photos across your multiple online accounts and your hard disk. If you want to see how good a Web application can be, take Picnik for a spin.

• 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.

You could use the software that came with the camera for some of this, but, in general, software created by hardware companies isn’t very good. Since most people use Windows computers, they will likely just dump the pictures into the My Pictures folder that Windows provides. But this folder was never meant for true photo organizing.

If you use an Apple Macintosh, you’re in much better shape, because Apple provides a very good built-in photo-organizing program called iPhoto. But iPhoto isn’t integrated with any of the popular online photo sites that let you store and share pictures. And, of course, it’s unavailable to the vast majority of people, who use Windows.

However, there’s a very nice photo-organizing program out there that’s free, works on both Windows and Mac and is closely integrated with one of the best online photo sites. It brings most of the best features of iPhoto to Windows users, and for Mac users, it offers tight integration with a Web-based photo site.

This free software is called EasyShare, and it comes from Eastman Kodak, though you don’t have to own a Kodak camera or printer to use it. It works with any brand of camera and printer to easily organize, email, print and touch up your pictures. And it’s closely linked to Kodak’s EasyShare Gallery online photo site, formerly called Ofoto, which is one of the best Web photo services and is free to use.

I’ve been testing EasyShare, on both a Windows and a Macintosh computer, and I like it. It’s the exception to the rule that hardware companies can’t create good software. EasyShare comes with all Kodak cameras and printers. Owners of other brands can download it by going to kodak.com and clicking on “Downloads & Drivers.”

Photo-organizing programs are different from traditional photo-editing software like Adobe’s Photoshop. Where traditional photo software is mainly about tweaking and perfecting your pictures, organizing programs are mainly about finding, arranging and sharing pictures, with a little light editing thrown in.

There are other popular Windows programs that aim to help you organize your pictures. Among the best known are Picasa, ACDSee and Corel Photo Album. Adobe had a good organizer called Photoshop Album, but it has since folded it into its editing-centric Photoshop Elements.

But most of these programs fall short of the combination of simplicity and power that Apple’s iPhoto pioneered. They often require users to know too much about the Windows folder and file system. By contrast, EasyShare, like iPhoto, frees you from the file system, relying instead on its own system for organizing your pictures.

As in iPhoto, a key feature of EasyShare is the virtual album, which doesn’t correspond to any folder on the hard disk. Any picture can appear in an infinite number of virtual albums without having to be copied or taking up extra harddisk space. For instance, a picture of Sally opening a Christmas gift in Providence, R.I., in 2005, could appear in albums called “Christmas,” “Sally,” “Providence trip,” “2005″ and so on.

EasyShare lets you burn CDs of your photos, easily email them to friends and print them in creative ways. It also has some very nice touch-up features, including a one-click fix function that previews changes by splitting the picture temporarily into “before” and “after” halves.

Kodak’s EasyShare on Windows

The Windows and Mac versions of EasyShare look very different, but they share the same basic commands and about 95% of the features. The Windows version has a few editing features the Mac version lacks, including editing of uncompressed RAW photo files. The Mac version also has some things the Windows version lacks, such as automated backups and the ability to create “smart albums,” which automatically gather up photos based on criteria you set in advance.

Once your photos are in virtual albums inside EasyShare, these albums can be uploaded to the online EasyShare Gallery. You can also designate pictures in any album as “favorites,” and they can be automatically synchronized with a favorites collection online.

Obviously, this integration with the online site is a business strategy for Kodak: Once your pictures are stored on its online site, Kodak hopes you’ll order prints and gifts made from them. But you don’t have to join the site to use EasyShare, even though the program will nag you to do so. And if you do join, the Gallery is free and very useful. It provides a safe backup for your photos and a way to share them without emailing copies all around. Instead, you send emails from the software that offer links to the photos on the Gallery.

If you’re getting a new digital camera or are just buried in pictures from an old one, Kodak EasyShare software is worth a try.

• Email me at mossberg@wsj.com.