Magic Trackpad Getting Jumpy? Here’s a Weird Fix

As you may know, Lion recently came out. Lion relies heavily on multi-touch gestures to be taken full advantage of. So I decided to break out the magic trackpad and try it out.

I’ve had many problems with the magic trackpad recently, mostly with it jumping around the screen a lot – I would touch it, and suddenly it would be on the other side of the screen. This time was no exception.

So why does my trackpad keep doing this? I’ve replaced the batteries, cleaned it off, and even tried someone else’s.

After a bit of research, I finally found the problem:

Time Machine.

I don’t know why, but after I read this I noticed that Time Machine was backing up. Hmm…. I stopped the backup and Voilla, the trackpad is back to its normal, behaving self.

This is going to get in the way, considering that Time Machine likes to back up every hour; make sure you keep an extra USB mouse on hand just in case.

To tell you the truth, I have absolutely NO idea why Time machine causes a problem with the trackpad. Time Machine connects over WiFi, and the Trackpad connects over Bluetooth. They’re totally seperate antennaes – why are they interfering with each other?

Although there is no explanation to this solution, it’s still a solution. So remember – if your trackpad is acting up, check to see if Time Machine is backing up. (HEY THAT RHYMES!)

9 thoughts on “Magic Trackpad Getting Jumpy? Here’s a Weird Fix

  1. The frequency used by WiFi and Bluetooth varies (depending on several factors) but they indeed can collide. The antennas on modern computers are so close each other and so receptive that it does not really matter much that they are separate, there can be interference.

    Another source for the issue could be XNU, the kernel of OS X. If kernel load is high, it can lead to stutter. Traditionally both networking and filesystem access have been rather taxing on OS X kernel. 

  2. True, but for some reason the trackpad doesn’t screw up if i’m downloading or uploading things to the internet – only when I’m backing up with Time Machine. It could be XNU, true – but I don’t think that a file upload really puts that much load on the kernel. And even if it did, why doesn’t this happen when I’m uploading/downloading things, and only when I’m backing up with Time Machine?
    Very strange indeed.


    When I have Airfoil going to my AirPlay speakers, it does the same thing – hmm.

  4. It is strange and I admit I’m mostly guessing. Downloading/uploading is usually such that you write/read one file or a few files at the time. The Time Machine backup will traverse several directories and use the FSEvents system to determine which files to upload. Doing such random access is more taxing to the filesystem and slower, especially if you’re using a traditional HD. 

  5. That is very true… Random access will definitely slow things down. However, I’m using an SSD.
    I don’t know if apple plans to fix this, but if they do I wouldn’t mind.

  6. INTERESTING. I had my trackpad replaced recently for the same reason. maybe I coulda saved myself the $90?

  7. 🙁 That’s too bad! I wish apple employees knew more of the little tricks that users find.

  8. By the way: Since Apple released an Mac OS X update to 10.7.1 this problem disappeared for me just after the installation. Give it a try…

  9. I thought that might be the case, but I only rediscovered this issue when I installed lion and started using my magic trackpad with it.

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