I'm running OS X Yosemite 10.10.1 on a mid 2012 13" MacBook Pro with the 2.5 GHz Intel Core i5 processor and 4GB of RAM. The hard drive (the 500 GB, regular HDD) was replaced about a year ago (close to 10 months after purchase) following a failure.

One morning, after waking up and waking the computer from sleep mode I encountered a strange amount of lag. It was bizarre because I was using the machine the night before without any problems, and now it was constantly stuttering while trying to play a movie on Netflix. Sound would play while the video froze every few seconds.

I restarted the computer, and the problem persisted. Moreover, it lags no matter what I do. iTunes can't make it through a song without freezing up 6-7 times, VLC constantly stutters too. The rainbow wheel pops up and spins any time I load a new page in Safari or Chrome, search with Spotlight, change pages in SimpleComic, change tabs in Finder, try and drag a file from one folder to another, etc.

It's constantly stuttering, freezing, and hanging any time I try and do just about anything. It usually only lasts 10-20 seconds, but it happens repeatedly. I've tried every remedy I know: restarting, repairing disk/permissions, turning off transparency, reinstalling OS X, restoring a Time Machine backup from before the problem, even clean reinstalling OS X. Nothing seems to work, there are no error messages, and I'm really annoyed.

I'd think it's a hardware problem, since a clean reinstall didn't work, but I ran the Apple Diagnostic Test and it found no problem. Moreover, everything works, just with crazy lag system-wide.

I'm wondering if anyone else has this problem, knows what it is, or if there's anything I can try that I haven't.


After a few tests, I've ruled out the logic board and HDD. I tried running the hard drive through an older Macbook, and it seemed to work alright (a little slower than normal, but it's a 2008 machine that hasn't been turned on in about a year so that's to be expected). I also started running OS X off an external hard drive, and it runs perfectly (which is why I think the logic board is fine).

Right now I think the issue stems from the SATA cable, which may be failing. I've ordered a replacement and I'll update this again once I've installed it.

Thanks for all the help so far!

  • you seem to have reset most things, but did you try PRAM & SMC?
    – Tetsujin
    Commented Nov 30, 2014 at 9:47
  • I did, unfortunately it didn't really do anything. :S I'm currently thinking it's a failing SATA cable, so I've got the system on "life support" so to speak--booted from an external HDD with OS X installed on a partition and it works--until I can get a replacement in. Commented Dec 3, 2014 at 0:16
  • Im reasearching to update my OSX as well 10.6.8 to 10.10 minimmum RAM might be the problem. generally more RAM = faster machine
    – user111438
    Commented Jan 28, 2015 at 7:20

7 Answers 7


It turns out that the issue here was a failing SATA cable. It hadn't totally kicked the bucket, hence the computer could still boot and run fairly normally from the internal hard drive. I believe the intermittent lag was caused by the faulty cable.

The good news is, replacing it was easy (albeit a little pricey at $40). It's only a few more steps than removing a hard drive, and iFixit has a nice guide for anyone who has this problem.

Be sure you know it's the SATA cable before replacing it. I ruled out the hard drive and logic board like this:

  1. Hard Drive - I tested my hard drive in another Macbook. You could also try a USB enclosure or, in a pinch, remove your optical drive and try it there.
  2. Logic Board - I installed OS X on a USB drive and booted from it. Performance was normal (expect it to be a little slower).

If you have a USB enclosure for your internal drive, you can rule these both out at once.

Thanks everyone for their comments. I hope this helps anybody who hits a similar problem.


try a new SSD, if you have the same problem you can return it and you'll know it's not the hard drive.

  • Thanks for the suggestion! I'd love to try that, but I don't exactly have $100+ to drop on an SSD right now. I mean, if I really had to (i.e., if my current hard drive totally failed) I would find a way, but hopefully it's onther problem. . . Commented Nov 30, 2014 at 3:44
  • i hear ya, but a good SSD could be one of the cheapest solutions... OWC has a 240gb for $159. good luck!
    – scoutelder
    Commented Nov 30, 2014 at 3:55
  • try creating a new user account and test if it runs any better.
    – scoutelder
    Commented Nov 30, 2014 at 18:26
  • I actually already tried that at a friend's suggestion. I ended up installing OS X on a partition on an external hard drive, and it runs fine. I also popped my hard drive into an older Macbook on a whim, and it seems fine too. I think the issue is probably with the SATA cable, and I've ordered a replacement. Commented Dec 3, 2014 at 0:14

How many of those apps do you use/keep open simultaneously? If the answer is "a lot", there's no way your RAM could support it. I'd recommend going to Activity Monitor and clicking on the Memory tab to see what your RAM usage looks like.

  • Not many, actually; I'm usually only using Chrome, sometimes with iTunes or Messages in the background. I tend to prefer an uncluttered system/workspace/etc. I've tried Activity Monitor and it seems like Chrome is using a lot of memory now, but I've tried running the system with Chrome uninstalled and still faced the same problem. Memory Pressure always looks really low, and Swap Usage is 0. Commented Nov 30, 2014 at 16:56

I had what sounds like a similar issue on same version of Yosemite and resolved using the following ...

WindowServer high CPU on Yosemite

Hope it helps.

  • Thanks for the tip! I'll try it later if I can and keep you updated. Commented Dec 3, 2014 at 0:18

Logic Board - I installed OS X on a USB drive and booted from it. Performance was normal (expect it to be a little slower).

How does this rule out a logic board problem? Aren't you just swapping one volume for another but still using the same logic board?

  • Read past the 'i also' bit
    – Tetsujin
    Commented Dec 16, 2014 at 12:54

I'm having exactly the same problem and i tried everything just like what you did. at last i brought it to apple care and it was the hard drive. it seems that our mac version is having problem with this version of osx. i replaced my Hard drive and every things runs back to normal


On reading the first post I was screaming at you hard drive cable! (I'm here too late) as they are always the cause on these machines from 09-12 it seems they fail and the Mac runs slow or you end up not being able to access the hard drive at all and get white screen with boot options on startup with no fix other than a new cable.

By the way have you noticed the dimming light on the front of the Mac when it's in sleep mode does not quite go completely out like the original but rather dims to a very low level instead? It's the only difference I can tell from the replacement oem part

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