And then this year everything changed. Apple Computer, the maker of the Mac, switched to the same Intel-made processors for which Windows was designed. The new Intel-powered Macs, which began shipping in January, still come with Apple’s own operating system, Mac OS X, which is more modern and more secure than Windows XP. But these Macs can now easily run Windows too, and they run it as fast as standard Windows-equipped PCs.

Why does this matter? It means that you can switch from Windows to the Mac and still use the one or two Windows programs you require that have no Mac equivalent.

Among the Mac models that can perform this feat are the iMac and Mac Mini desktop computers and the MacBook and MacBook Pro laptops. Apple’s most powerful model, the PowerMac tower, is likely to be converted to the Intel chips by the end of the year, after which it, too, will be Windows-capable.

There are two options for running Windows on the Mac. They take different approaches, but in my tests, both have proved to be fast, stable and widely compatible with Windows software. One, from Apple itself, is free. The second, from a small Virginia company called Parallels, costs $79. But each carries an additional cost: You have to supply and install your own copy of Windows, which can run $200 or $300, depending on which version you choose.

The Apple system, Boot Camp, uses a technique called Dual-Boot. It splits your Mac’s hard disk into two sections, or partitions — one for the Mac operating system and all its programs and files, and one for Windows XP and all its programs and files. You can start, or “boot up,” the Mac in either operating system, but you can’t run both simultaneously. To switch between a Mac program and a Windows program, you have to reboot the computer.

The Parallels system, called Parallels Desktop for Mac, uses a technique called Virtualization. It creates a virtual Windows computer inside a window within the Mac operating system. Parallels runs Windows a tad more slowly than Apple’s Boot Camp, but allows you to run both operating systems, and compatible software, simultaneously. You can switch rapidly between the two environments without rebooting. I’m writing this paragraph on a MacBook Pro laptop, but I’m not using any Mac software to do so. Instead, I’m using the Windows version of Microsoft Word, which runs inside Parallels Desktop.

For this paragraph, I’ve switched back to the Mac side of the computer and am using the Mac version of Word. And I copied the previous paragraph from the Windows side and pasted it into the Mac document. It was fast and flawless.

Each approach has its strengths as well as weaknesses.

Apple’s Boot Camp turns the Mac into a true, no-compromises Windows PC-just like a Dell or Hewlett-Packard computer. When you boot up the Mac in Windows, no trace of the Mac operating system is running; Windows has all the hardware and all the memory to itself. In my tests, Macs running Windows under Boot Camp were wicked fast and handled every single program I tried, including Microsoft Office for Windows, the Internet Explorer Web browser and various games. The downside is that pesky need to reboot when switching operating systems.

Parallels Desktop is much faster than the old software for running Windows on pre-Intel Macs, a Microsoft product called Virtual PC. That’s because Parallels makes use of special virtualization features built into the Intel chips. And it has the great advantage of running Windows applications at the same time you are running your Mac programs. But while quite fast, Parallels can’t match the speed of Windows running under Boot Camp, because it must share hardware and memory with the Mac operating system. Also, Parallels won’t work with certain high-end Windows games, and it can have trouble recognizing some USB drives and CDs. In my own tests, Parallels did handle everything I threw at it, but I introduced only simple games. Everything ran as fast as it would on an average Windows PC, though not as fast as the programs ran under Boot Camp.

Because Windows is much less secure than Mac OS X, when you run Windows on a Mac, you have to take the same precautions you would with a standard Windows PC. That means you need to install and run both antivirus and antispyware software that is generally not needed under the Mac OS.

Apple’s approach is more secure than Parallels’s in this regard — with Apple’s Boot Camp, Windows can’t see or access your Mac folders or files. That means any malicious software running in Windows can’t erase or damage your Mac files. Parallels, on the other hand, optionally allows you to share folders between the two operating systems; if you enable this feature, you could give a malicious Windows program an opening to damage or spy on the files on the Mac side.

Installing both programs is fairly easy, but it’s a multistep process. With Apple’s system, you first download and install Boot Camp. Then, using Boot Camp, you divide your hard disk into Mac and Windows partitions. Next you create a CD to be used later, under Windows, to install software “drivers” that Windows will need to control all aspects of the Mac’s hardware. Then you install Windows. Finally, you install the CD you created.

Note that Boot Camp requires a full retail version of Windows XP, called “SP2.” You can’t use any other version of Windows, and you can’t use an upgrade edition, which requires an earlier version of Windows to be present on the machine.

Parallels allows you to install any version of Windows, even a very old one. But if you use Windows XP, you will in most cases also need a full, retail version, not an upgrade package. You first must buy and install the Parallels program, which creates an empty “virtual machine.” Then you install your copy of Windows inside Parallels. Finally, to enable certain key features, you have to install a program called Parallels Tools, which is included.

This all sounds harder than it is. In each case, the whole process took me about an hour and required no technical skill.

And it’s worth the effort. Boot Camp and Parallels have turned the Intel-based Macintosh into the only computer that can run nearly every popular software program, whether it was written for Windows or the Mac. On the same computer you can edit photos in Apple’s iPhoto program and check your e-mail in Microsoft’s Outlook — simultaneously, if you choose Parallels. Now, that’s progress.

The daunting security problems that have plagued Windows have also prompted many of its users to take a serious look at the Mac. This trend has been further reinforced by the “iPod halo effect,” in which Windows users who own and love Apple’s iPod music players are willing to consider the company’s other products. As a result, Mac sales, while still relatively small, have been growing much faster than overall personal computer sales.

Are you among the PC majority considering a switch to the Mac? Then you probably have some important questions.

How do Macs compare in quality with Windows PCs?

I believe that, at the moment, Apple makes the best computers, and the best operating system, for mainstream consumers doing typical tasks — e-mail, Web surfing, office — productivity functions such as word processing and presentations, photo organizing and editing, playing and collecting music, and editing home video.

Of all the major computer makers, Apple is the most focused on consumers and small businesses. Most make the bulk of their money, and take most of their cues, from the information-technology departments of large corporations.

Apple’s iMac G5 consumer desktop is, in my opinion, the single best home computer on the market. Its PowerBook laptops are among the top portables.

Do Macs run Windows and Windows software?

No: Out of the box, Macintosh computers run only Apple’s own operating system, called OS X, and software written by Apple and other companies that is designed to run on OS X.

You can rig a Mac to run Windows and Windows programs by installing a special, $250 Microsoft program called Virtual PC, which creates a virtual Windows computer inside the Mac. But I don’t recommend this for frequent use, because the faux Windows computer it creates is relatively slow and is susceptible to the same viruses and spyware as a real Windows machine.

How does Mac software compare with Windows?

The Mac’s OS X operating system, the latest version of which is called Tiger, is far better than Microsoft’s aging Windows XP and already boasts many of the key features Microsoft plans to include in its 2006 version of Windows, called Vista. And the Mac comes with an excellent suite of free software that’s generally superior to comparable Windows programs that cost extra.

Out of the box, the Mac has better photo, music, video and DVD — creation software than any Windows computer I’ve seen. It has a better free email program and Web browser than Windows does, a better free word processor and much better search capabilities.

About the only software a typical consumer would have to buy for a new Mac is the Mac edition of Microsoft Office. It includes versions of Word, Excel and PowerPoint that are very similar to their Windows counterparts, and a program called Entourage that is different from Microsoft Outlook but performs the same functions.

Are Macs more secure than Windows PCs?

Yes. Since the OS X operating system came out in 2001, there has never been a report of a successful virus for it — that is, a virus that has infected numerous computers, and spread from computer to computer, outside of a lab. And there is little or no known spyware for the Mac. By contrast, there are tens of thousands of viruses for Windows and untold numbers of spyware programs. Just as regular Windows programs can’t run natively on a Mac, none of these malicious Windows-specific programs can run on a Mac either.

The Mac isn’t invulnerable, but it has better built-in security than Windows, and such a small market share that virus and spyware writers haven’t targeted it yet. As a result, most Mac users have been able to dispense with running the morass of security software that Windows users must employ.

Are Mac files compatible with Windows files?

Yes. Unlike older models, the current Macs have been specifically designed for compatibility with Windows PCs. The Mac OS and software can handle, without translation or conversion, all of the common types of files you use on a Windows PC. You can copy to a Mac all your pictures, MP3 music files, text files and Adobe PDF files, and they will open right up in Mac programs. There are also free Mac versions of the Real Player and Windows Media Player, and of Adobe Reader.

Microsoft Word files also can be opened, edited and created in Apple’s free, built-in text editor. And if you buy Microsoft Office for the Mac, all Office files, including Word files, Excel files and PowerPoint files, can be opened, edited and created on the Mac. Office files created on the Mac can be opened and edited in Windows Office, and vice versa.

Some specialized files created by particular programs, like database files or financial files, won’t be usable. For instance, the Mac version of Quicken is quite different from the Windows version and uses a different file format.

For occasional use of these programs, you can install Virtual PC.

In addition, nearly all keyboards, mice, monitors and printers made for Windows computers can be used with a Mac, if they connect via the industry-standard USB or FireWire ports. Macs can also share networks with Windows PCs and even look into the hard disks of Windows computers, and vice versa.

Is there anyone who shouldn’t consider a Mac?

Yes. Serious game players should stick with Windows PCs, which are much better game platforms and can run many more game titles. People who use specialized software or custom corporate software for which there isn’t a Mac equivalent should stick with Windows. While the Mac has rich offerings in mainstream software categories, it has only a fraction of the niche software and specialized business software that Windows does.

Also, you should stick with Windows if your home computer choices are dictated by your company’s IT department and the IT department is ignorant of or hostile to the Mac, as so many are. Although modern Macs are designed to access corporate Windows networks, and many do, if your IT department won’t help you with the transition, it’s not worth the headache to switch to the Mac.

Ten years ago, when Apple was stagnant and its products troubled, I recommended that consumers shun the Mac. If Apple’s quality and innovation slip, I might revert to that position. But for now, the Mac is the best computer, with the best operating system and the fewest security problems, for average consumers.