If you use Parallels on a Mac, you may notice that Parallels consumes massive amounts of RAM; even above and beyond the amount you gave the client operating system. What’s worse is the performance hit lingers even after the application is closed. This is due to a bug in the Parallels software. Parallels tries to cache your client OS in RAM; a redundant cache considering that the client OS has its own caching mechanism. Luckily there is a quick and easy way to fix this bug.

If you’re using the latest final version of Parallels, you can download PD Tweaker. PD Tweaker uses Unsanity’s Application Enhancer to modify the behavior of Parallels while it’s running in RAM, changing the way Parallels caches files. While this does consume a little bit of resources when Parallels is running, the amount of resources it prevents Parallels from using is above and beyond anything PD Tweaker takes up.

If you’re using the latest beta version of Parallels, the Parallels team has fixed the caching bug, but they haven’t enabled the fix by default. I know it doesn’t make any sense, but that’s what the Parallels team did. Fortunately it’s only a matter of changing a checkbox, which I’m going to show you how to do now.

The first thing you’ll want to do is load up Parallels. After Parallels is loaded and your Virtual Machine is open, click on the Edit button on the bottom of the VM window.

This will bring up the Configuration Editor. In the editor, click on the VM Flags tab. On the bottom right of this tab you’ll see a box entitled Cache Policy. You’ll have two options: Virtual Machine and Mac OS X, with Virtual Machine as the default setting. To fix the caching bug, simply change the option from Virtual Machine to Mac OS X and save the options. Now Parallels will stop redundantly caching the client OS.

Let’s hope that the Parallels team changes the default option to Mac OS X in the final version. I know I can’t see any situation where you would want to have the client OS consume all the resources of a machine. If you’re going to do that, why would you run Parallels in the first place? It would make more sense to use a dedicated solution like Apple’s Boot Camp.

Well, I’m not going to continue to go on about the poor choice of the Parallels team. Just be sure to either use PD Tweaker or change a simple check box. Then you’ll be able to enjoy both a speedy client operating system as well as have your host OS, Mac OS X, run as if nothing crazy was going on in the background. Digg this.