When the first version of Parallels Desktop hit the streets two years ago, it was just amazing. The software allowed you to run Windows, along with its applications, on Mac OS X. Mac users just flipped for it.

Parallels lets you run Windows (shown here) or Linux on Mac OS X.
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But with Parallels Version 3, introduced last year, the company seemed to have lost its way. The software was slow and buggy. Users put up with the problems for a while, because it was the only product of its kind, but when competition emerged, in the form of VMware Fusion, users switched to the new product. VMware even ran its own "switcher" marketing campaign, like Apple did against Windows.

Today, I know about a dozen people who use the VMware product. I only know one person who still uses Parallels. He complains about it a lot.

This month the company (also called Parallels) introduced Parallels Desktop 4, which it says has significantly improved performance and stability over the previous version, and a few new features.

In other words: Parallels is back from its long spree in Vegas, with a bouquet of roses in hand and a hangdog expression its face. It's promising to be good. It wants us to take it back.

Should we open our hearts and give the relationship with Parallels one more try? Or should we kick it to the curb?

I downloaded the software and put it through its paces to find out whether the new version is any good.

What Is Parallels?

Parallels is an example of "virtualization" software. Virtualization software makes one computer look like two or more computers, which turns out to be all kinds of useful.

In the datacenter, virtualization software lets companies make more efficient use of their servers. On the Mac, virtualization lets you run other operating systems in addition to Mac OS. Most commonly, you'll use Mac virtualization products like Parallels to run Windows, but the products also runs Linux.