Discover what's slowing down your Mac

Do you know which applications use the most processing power in your Mac? Which apps does your iMac or Macbook spend the most time processing? It might be useful to find out and if your computer is running more slowly than you think it should be, it might enable you to identify the problem.

The obvious tool to use to find which apps use the most processing power is Activity Monitor and this can be started from the Applications/Utilities folder on the disk drive. There are five tabs in the toolbar at the top (four if you are not running the latest version of OS X), and the one to select is CPU.

Activity Monitor

The %CPU column is displayed by default and this shows the workload each application is placing on the processor right this second. Click it to sort the column into ascending order and click it again to sort into descending order. This is best as it puts the apps that are working the processor the most at the top.

A live display of CPU usage is useful, but there is another useful statistic that you should look at. This is the total time the processor has dedicated to an app. An app might be using the CPU very lightly right now, but it could have been hogging the processor for the previous hour. The live %CPU column would not tell you this. What you need to look at is the CPU Time column.

If this is not visible in Activity Monitor, go to the View, Columns menu and tick CPU Time. Click the column header to sort the apps into ascending order and then again to sort into descending order so the most demanding apps are at the top.

The apps that use the most CPU time are the ones that you have been using the most, obviously, but sometimes you can see other things in there that are not visible on the screen - apps and services that run in the background. An unusually large number might indicate a problem or at least a reason why your Mac has been running slowly.

Monitor activity from the Terminal

Underneath the pretty interface, OS X is very similar to Linux and there is a command line tool for monitoring system activity from Linux that works on your Mac too. It is called top and if you want to try it, go to the Applications/Utilities folder and run Terminal.

In the Terminal window, just type top and you will see what looks like a text-based version of Activity Monitor. Not all processes are displayed, so if you want to see more, drag the bottom of the window down to enlarge it.

Related: What is the 'defaults' Terminal command?

At the top it reports the number of processes, the processor load average, physical memory used and unused, disk activity and so on. In the bottom half of the display is the list of processes, %CPU, CPU time, memory and so on. It is live and it updates every second or two. When you have seen enough, press Q to quit and return to the command prompt in the Terminal window.

Terminal in OS X

Here is a more complex example of top usage, taken from the OS X manual.

top -o cpu -O +rsize -s 5 -n 20

All those parameters make the command look complicated, but it isn’t really. Here is a description of each part:

-o cpu = sort apps by CPU usage in descending order

-O +rsize = secondary sort apps by memory usage

-s 5 = update every 5 seconds

-n 20 = show the top 20 processes

Related: Solve Spotlight indexing problems with Terminal commands



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