Why is my Mac running so slow? [MacRx]



Macs are solid machines, but (like many of us) they have a tendency to slow down and get more lethargic over time.  Launching and switching programs takes longer, the dreaded Spinning Beach Ball appears more often, and soon even simple tasks become arduous.  What’s going on?

Many things can decrease performance, but several culprits are common: not enough disk space, not enough RAM, and running too many apps at once.  I see these in my consulting business regularly.

Not enough free disk space

Modern Operating Systems use the hard disk for temporary storage.  Cache files, temp files, and (most importantly) virtual memory swap files help the OS juggle finite RAM resources among the many apps and tasks which are running.

When your hard drive fills up too much, system performance suffers.  You can see how much space is left on your drive by looking at the bottom of a Finder Window, or clicking on your drive on the desktop and choosing File –> Get Info (or CMD-I).

A general rule of thumb is to keep at least 10% of your hard drive free at all times, with an absolute minimum of 5GB free (slightly less for PowerPC systems).  Drop under this and your Mac is wheezing up the stairs; with less than 1GB free it’s gasping for air on the floor.  When space completely runs out, accessing even non-boot drives becomes tricky.

To free up space delete unneeded data, including old downloads, installers and .zip archives.  There are several Gigabytes of files in your top level /Library/Application Support folder for things like Garage Band, iDVD, etc., which you can delete if you don’t use these applications.  You can also move files to external drives and delete the originals.

When you can’t clear enough to make room, it’s time for a bigger hard drive.

Not enough RAM

Your Mac uses RAM to store user data that the CPU is actively using; this type of storage is fast and efficient, but in limited capacity compared with slower disk storage.  The more RAM you have the more data can be made quickly accessible to the processor, with less need to read and write to disk. You can see how much is installed in your system under the Apple Menu –> About This Mac.

Apple ships most Macs with less RAM than you ultimately need. For Leopard and Snow Leopard on Intel-based Macs, 2GB is a good practical minimum.  For Tiger on Intel (yes, people are still using this), 1GB minimum is recommended.  More is always better.

PowerPC Macs generally have half the RAM requirements of Intel machines.  For Leopard on PowerPC, go with 1GB minimum; for Tiger, 512MB.  Anything older than Tiger or a G4-based Mac is impractical these days, particularly for internet access.

Running too many applications

Compounding the demands on your RAM are the multiple programs we, the pesky users, run on our machines.  Generally the more things you run at once, the more RAM you should have.

This problem has become more common as people switch to the Mac from Windows.  Unlike on a PC, closing all the windows for a program does not quit the program on the Macintosh.  You need to choose File –> Quit (or CMD-Q) to exit the application.  If the dot is still glowing underneath a program’s icon in the dock that means it’s still running.

Another possibility is an unused app that has crashed in the background.  You may not see any visual indication of a problem, but the system may suddenly get very slow or erratic.  You can use the Activity Monitor app (inside Applications –> Utilities) to look for suspect processes.

Quitting unused applications will free up RAM and improve performance. I’ve come across clients complaining about bizarre behavior on their Macs, only to find thirty apps running simultaneously!  Quitting (or Force-Quitting) most of them substantially improves performance.  As does my last suggestion, which is probably the Most Often Suggested Tech Support Fix:

Reboot once in a while

Rebooting your Mac is the computer equivalent of a good night’s sleep and a hearty breakfast.  RAM is cleared, processes reset, and you start with a clean slate.  Modern Macs run a version of UNIX and are very stable and reliable, but still do need a restart from time to time.

I generally tell my clients to reboot every few weeks, or whenever their system is acting strange.  This isn’t a hard and fast rule but going months at a time will most likely cause problems.  If your Mac doesn’t want to shut down or restart normally, other problems are likely looming.

These are some common causes of performance problems, not a comprehensive list.


Daily round-ups or a weekly refresher, straight from Cult of Mac to your inbox.

  • The Weekender

    The week's best Apple news, reviews and how-tos from Cult of Mac, every Saturday morning. Our readers say: "Thank you guys for always posting cool stuff" -- Vaughn Nevins. "Very informative" -- Kenly Xavier.