Slow OS X computer

OS X computers (Macs and Macbooks) can become sluggish with time. In this page we cover some of the ways you can recover lost performance.


This page gives guidance on how to diagnose problems causing a OS X computers to run slowly, and what to do about them.


Remember to back up your data, and check, and if necessary repair, your hard disk before attempting anything else.
Consider anti-static precautions when handling RAM or deep disassembly, especially when humidity is very low, or at least touch an earthed metal object before starting.


Probably the most common reason people ditch their old computer and buy a new one is not that the old one is broken in any way, but that it’s simply running slowly. There are a few key things that are well worth trying before giving up on your trusty Mac, but before you attempt anything, always back-up your files.


Is your system regularly backed up? If not, you're lucky if you haven't yet lost any data. OS X includes a backup feature called Time Machine. You will need to connect an external hard disk, use a Time Capsule, or have a networked disk to use it.

Verify disk

Verify the disk in Disk Utility (in Utilities). If problems are found, you should repair them as soon as possible. Any further use of your Mac may further damage the file system. You cannot repair a disk from which you are running the full OS X and there are several ways to be able to perform a repair:

  • One way to repair the disk is to reboot in single user mode (holding down Cmd-S after the chime until text appears on the screen) and at the prompt type (without the quote): '/sbin/fsck -fy'. Repeat this command until nothing is fixed.
  • A simpler alternative for OS X up to 10.6 inclusive is to download and install AppleJack. After rebooting in single user mode, run 'applejack' and at least run option 1.
  • From OS X 10.7 onward, you can boot from the recovery partition by holding down Cmd-R until the Apple icon appears, and then run Disk Utility and click on Repair Disk.
  • Yet another option if you have your OS X install DVD or USB handy is to boot from it and instead of installing the system go to the Utilities menu to run Disk Utility.

Check available disk space

There should be approximately 10% of the disk free for the system to work correctly. This is a general rule that applies to most operating systems.

Either use Disk Utility or Ctrl-click on the disk in the finder and select Get Info to find the disk size and how much of it remains available.

To help find files taking a lot of space, use tools such as GrandPerspective. Be careful to delete files that you know are safe to delete. Movie files that you do not want to keep are good candidates to delete.

Make sure your system is up-to-date

Run Apple / System Update and install any update.

In Firefox / Tools / Add-ons, select plug-ins and click on 'Check to see if your plugins are up to date'. Update all plug-ins identified as vulnerable, in particular Flash. Note that on OS X 10.6 this states that QuickTime Plug-in 7.6.6. is vulnerable when it is the correct and latest version for this version of OS X. U

Remove automatic launching of applications no longer used

Login items

In System Preferences / Accounts / Login Items, delete login items for applications you do not use any more or that you do not need to launch at boot. If you are not allowed to delete login items, click on the lock in the bottom left of the window and enter an administrator username and associated password.

Other ways programs can be launched automatically

Check for applications and plug-ins no longer used in the directories below. Instead of just deleting them, you should move them to a directory with a similar name ending in '(disabled)' so you can correct any mistake you make. When wondering what a file is doing, the Get Info may tell you the company that created it and the version, also a web search can help you identify what a file is and whether it is necessary or it is safe to delete. Note that not all these directories may exist. Do not move or delete any of these directories.

  • ~/Library/Input Methods
  • ~/Library/InputManagers
  • ~/Library/Internet Plug-Ins
  • ~/Library/LaunchAgents
  • ~/Library/LaunchDaemons
  • ~/Library/Input Methods
  • ~/Library/StartupItems
  • /Library/Input Methods
  • /Library/InputManagers
  • /Library/Internet Plug-Ins
  • /Library/LaunchAgents
  • /Library/LaunchDaemons
  • /Library/StartupItems

Some applications can also be launched automatically when right-clicking, so check for old entries that may no longer be relevant in:

  • ~/Library/Contextual Menu Items
  • /Library/Contextual Menu Items

To reveal your home library (~/Library/) in OS X 10.7 and more recent, open Finder. On its menu bar,select Go to reveal the drop-down menu and then hold down the Option key (also known as Alt key) and the ~/Library folder will appear so that you can select it.

The application KnockKnock can help you identify items no longer used that you may want to delete. Many items the application lists are fine, so use it only as an aid to find applications that are launched automatically and then either recognise items that you installed and no longer need or do more research before deciding whether to keep or delete them.

Only if you're trying to prevent a no longer used application from starting and the above steps were not sufficient, consider whether you may need to delete files in similar directories in /System/Library/ or one of its subdirectories.
Be extremely careful in changing anything under /System as this can easily stop your machine from working. Do check the web in case of doubt and only delete things when you fully understand what you are doing. Proceed under /System/ only with extreme caution.
RIM BlackBerry synchronisation as well as kernel extensions for some wireless modems are examples of applications that sometimes install files under /System/.

Upgrade apps that were written for PowerPC

As Macs are now equipped with Intel processors, old applications that were written for PowerPC require the Rosetta subsystem to emulate the PowerPC processor. This is inefficient and uses more memory. Also Rosetta is no longer supported from OS X 10.7, so any PowerPC only application will stop working when updating the operating system or purchasing a new Mac.

To identify apps that are PowerPC only, select Apple / About This Mac, then click on More info. In the Contents left window, select Software / Applications. Click on the column header Kind to sort by kind. Then move the list to find which apps are still PowerPC only.

If you have PowerPC apps, check if recent upgrades are available. Upgrades for commercial apps are likely to come at a cost. Also consider alternatives (e.g., OpenOffice or LibreOffice for Microsoft Office, Gimp for Photoshop, etc.); alternativeTo may help. A good website to discover OS X software is MacUpdate.

Increase memory

Adding memory is the cheapest and most efficient hardware upgrade to speed up any machine. To figure out how much memory and which type you can put in your machine use the Crucial System Scanner. You can either purchase memory from Crucial or elsewhere as long as you get the exact same type of memory as suggested by Crucial.

To figure out how to open the Mac to install the memory use the relevant iFixit guide.