For mainstream computer users doing typical tasks, Apple Computer’s Macintosh models have huge advantages over the prevalent Windows computers from companies such as Dell and Hewlett-Packard. The Macs have sleeker hardware designs, a superior operating system, much better built-in software and virtually no exposure to viruses and spyware. Apple’s flagship model, the iMac, is the best consumer desktop on the market.

But there’s a big barrier for Windows users tempted to switch to the Mac: software. While there are thousands of programs for the Mac’s operating system, called OS X, potential Mac buyers often find they have one or two Windows programs they must use that have no Mac equivalent.

Last week, Apple took a historic, and potentially huge, step toward removing that obstacle. It introduced free software that makes it easy to install and run Windows on the latest Mac models as a complement to the Mac operating system. With this new software, called Boot Camp, you can turn your Mac into a fast, full-fledged Windows computer for those occasions when you must run a Windows program. That makes the iMac, the Mac Mini and the MacBook Pro laptop the only computers in the world that allow mainstream users to run both operating systems at full speed.

I’ve been testing Windows on a new iMac for several days and it runs perfectly, just like a stand-alone Windows PC.

In Windows mode, the iMac was blazingly fast – far faster than my two-year-old HP Windows computer. And every function of Windows I tested, including Web browsing, e-mail and music playback, ran flawlessly.

In fact, I wrote this column in Windows on the iMac, using the Windows version of Microsoft Word. And I e-mailed it to my editors using Outlook Express, the built-in e-mail program in Windows. When I was done using Windows, I just restarted the Mac and the machine turned back into a regular Macintosh, running the Mac operating system and Mac software.

All this is possible because the latest Macs use the same Intel chips as Windows machines. Boot Camp runs only on these new Intel-based Macs, which have been available since January. Older Macs can also run Windows, in a fashion, but only via a clumsy Microsoft program that creates a painfully slow “virtual” Windows computer that can’t handle some demanding programs, particularly games. By contrast, with Boot Camp, the new Intel-based Macs can become true, fast, full-fledged Windows computers that are essentially identical to standard Windows computers, yet still retain the ability to operate as normal Macs.

It’s important to note that Apple isn’t abandoning its OS X operating system or adopting Windows. The company says it won’t sell, preinstall or support Windows. In fact, while Boot Camp is free Apple software, anyone using it must supply his or her own copy of Windows. With Boot Camp, you could choose to run a Mac solely as a Windows machine, with good results. But Apple doesn’t expect many people to do this. Instead, it assumes Boot Camp users will still use the Mac operating system and Mac software 90 percent of the time, switching into Windows mode only to run a few Windows programs. Some customers may never use Windows on their Macs, and just see Boot Camp as a sort of insurance policy that allows them to switch to the Mac without fear that they’d lose future access to Windows programs.

Until now, subtle hardware differences between Mac and Windows made it impossible to simply buy a copy of Windows and install it on a Mac, even the new models using Intel chips. Apple’s Boot Camp allows Windows to overcome these hardware differences, and also includes “drivers” – hardware-enabling programs – so that Windows can work smoothly with Apple keyboards, video systems and networking hardware.

Because the Mac becomes a true Windows computer when in Windows mode, it is susceptible to all of the viruses and spyware that plague regular Windows machines, but not Macs running the Mac operating system. While these viruses can’t infect the Mac side of the machine, you do have to install antivirus and antispyware programs on the Windows side.

To install Windows on a Mac with Boot Camp, you first must upgrade to the latest version of Mac OS X and perform what’s called a “firmware update.” Both are easy.

Next, you download the Boot Camp program and install it. Boot Camp first guides you through the process of burning a CD with driver software you will later install in Windows. Then it lets you divide the hard disk into separate Mac and Windows partitions. Finally, it starts up your Windows installation disk.

There’s one dangerous step in installing Windows. In one of the screens of the installation disk, where you are asked which hard-drive partition will be used for Windows, you must select “C.” If you choose wrong, you could obliterate your Mac operating system. I recommend downloading and printing out Apple’s Boot Camp Installation Guide, which has a picture of this screen.

But these are minor issues. All in all, Boot Camp works really well. Whether you want to run Mac or Windows programs, an Apple computer may be the only computer you’ll need.

Walter Mossberg writes about personal technology for The Wall Street Journal.