When Apple switched to Intel processors, Windows switchers as well as Mac users who needed to run the occasional Windows app rejoiced.

That’s because the chip switch was soon followed by the release of virtualization software that would let those users run Windows as if it were just another application on their Macs. While those first virtualization apps didn’t support all of Windows’s features and weren’t terrifically fast, they were miles better than the Windows-emulation programs that had previously been available for the PowerPC chip.

Since then, however, virtualization apps for the Mac have matured a lot. Four main options are now available: two commercial virtualization apps (Parallels Desktop for Mac and VMware Fusion), an open source alternative (VirtualBox), and another solution that lets you install Windows apps without installing Windows (Crossover). Those first two options are the most popular—and, for most users, the most sensible—alternatives.

I’ve reviewed many generations of Parallels and Fusion, so I’ve seen them develop. The advances they’ve made have been amazing. The two developers have pushed each other hard, and their products have leapfrogged each other to introduce new features and improve performance, resulting in two excellent alternatives. Running the current generations of these two virtualization programs—Parallels 8 Desktop for Mac ( ) and VMware Fusion 5 ( )—on one of today’s ultrafast Macs, only the most hardcore Windows users will feel the need to reboot into Boot Camp to run Windows natively.

Another result of this competition is that the two programs have evolved into near twins of each other. They offer similar features, similar performance, and at times, even look similar. There are a few differences, though, and that’s what I focused on in assessing the latest versions of each.

Opening and closing

The two virtualization apps do differ in speed—not the speed of the virtual OSes themselves or the apps in them, but the speed with which they open, sleep, resume, and shut down those OSes. In some very simple testing, I found that Parallels is notably faster at each of those tasks, but particularly at suspending and resuming. If you need to open and close virtual machines all day, these time savings could add up.

Both virtualization apps are relatively stable. I didn’t have any outright crashes in either, but I did experience some minor oddities in both. In Fusion, for example, entering and exiting full-screen mode causes more flicker and redraws than it does in Parallels. When using Parallels, however, I had some apps fail in Windows (which didn’t happen in Fusion), and there were times where I simply couldn’t type my password at the Linux login prompt.

Virtualizing Windows

While both Fusion and Parallels support literally hundreds of guest operating systems, most users will be employing them to run one or more flavors of Windows. Overall, both do an excellent job.

In earlier reviews, I found that both Parallels and Fusion do well running earlier versions of Windows, so this time I focused on the upcoming Windows 8. For testing purposes, I used the final Windows 8 Developer Preview (which should be identical to the consumer version due out soon). Both handle it well, for the most part. (Note: What used to be called the Metro interface in Win 8 is now usually just Start or, occasionally, the Windows 8 UI.)

For the traditional Windows interface (the Desktop button in Start), both apps run Windows as well as their predecessors. Office applications run without delay, and I never felt as if anything was lagging in either program. The Windows interface itself was fast and fluid, Web browsing was trouble-free, and the two email apps I tried worked fine.

Windows 8, running inside VMware Fusion 5.

Start apps—the shiny new full-screen apps for Windows 8—also ran fine, as long as I was using them while I had Windows running in each virtualization program’s “windowed” mode (meaning that Windows itself, rather than each Windows app individually, got its own OS X window).

Trying to use Start apps while in Coherence (Parallels) or Unity (Fusion) modes (which give each Windows app its own OS X window) had its challenges. It can be done in Fusion, but only if you run one Start application at a time. If you launch another, it replaces the currently running app.