About

PD Tweaker is an Application Enhancer (APE) plugin that addressed a few shortcomings in the initial release of Parallels Desktop (build 1848) for Intel-based Macintoshes.

PD Tweaker is no longer necessary with the latest release of Parallels. Both features of PD Tweaker have been incorporated into Parallels Desktop for Mac, but you need to make some configuration changes to enable them.

The original PD Tweaker page is still available in the archives.

Configuring Parallels Desktop

Parallels Desktop for Mac (build 1940) still doesn't default to best real-world performance. But at least they added a checkbox to let you fix it manually.

Here's how to set it up to get faster cache behavior:

  1. Shut down your VM if it's running.
  2. Open the property pages by hitting the "Edit" button at the bottom of the window.
  3. Select "Options" from the list at the left.
  4. Select "VM Flags" from the list at the right.
  5. Under "Cache Policy", select the "Mac OS X" checkbox.

Here's a screenshot of the correct setting:

Parallels Desktop configuration dialog

Questions

I don't quite understand the logic that Parallels used here, where they default to the behavior that's incorrect for most users.

Optimizing the cache for best performance of the VM makes sense if you do nothing on your computer except run Parallels. But outside of Parallels' own developers and testers, that's got to be a tiny percentage of the user base. If all you do is run Windows, why not just boot into it directly? Because you want to use your Mac as a Mac, obviously.

It also might seem like a good idea if the engineers are too focused on microbenchmarks. Windows boot time is indeed faster (after the first time) if you fill up your RAM with HDD blocks. But the performance of the rest of your Mac suffers horribly. If you do that, you're getting too focused on one tiny piece of the problem and completely losing the big picture. "Can't see the forest for the trees," in other words.

While micro-benchmarks can be very useful, they are often abused and lead directly to harmful premature optimization. Think about it: is boot time an actual problem? I doubt it. I tend to boot my virtual machine once and then leave it running.

Thanks to all who used and enjoyed PD Tweaker.