See what's slowing down your Mac with activity monitors

Some applications slow down the Mac by using too much processing power, too much memory or constantly accessing the disk. See how to use Activity Monitor, TOP and XRG to find the problem apps.

Do you know which applications use the most processing power in your computer? Some apps seem to demand more of the CPU than others and when the usage is high, the Mac can slow down. Which apps does your iMac or MacBook spend the most time processing?

Apps that drive the CPU hard cause the Mac the get hot an heat is a killer of electrical components. Don'ty worry, there are systems in place to prevent heat damage, but it is best not to test them. One of the ways macOS copes with execessive heat is to slow the CPU down, which reduces the performance of the Mac. Chill your Mac by closing or avoiding apps that use too much CPU.

Sometimes apps use too much memory and when this happens, the Mac can slow down as it uses the drive as an extension to memory. An SSD is fast, but is several times slower than RAM, so even on a new Mac it is best to avoid apps that use too much memory.

A RAM hog on an old Mac with a hard disk drive is a performance killer and you will spend a lot of time looking at the spinning beach ball as you wait for apps to do even the simplest thing when all the memory us used up and macOS starts using the disk drive as memory storage. Which app uses the most memory? It might be useful to find out.

SSDs have solved a lot of performance problems that would seriously affect old computers with mechanical disk drives, however, SSDs have a limited number of writes and a heavy user of the drive could shorten its life, but which apps are using the drive too much?

If your computer is running more slowly than you think it should be, an activity monitor can help you to identify the problem. Also read Find out what is slowing down your Apple Mac and how to fix it.

Monitor CPU, memory, disk with Activity Monitor

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.

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. It is best to sort with the apps that are working the processor the most at the top.

In the screenshot above GIMP is running the CPU at 53.9%. Is this a problem? When an app uses a lot of CPU, it could be a problem.

Not in this case though. I gave GIMP a huge photo to process, then quickly took the screenshot, but sometimes apps crash and show anywhere up to 100% CPU usage, and apps that should not even be working hard sometimes use a lot of CPU power. Close them or avoid them. Sometimes you might need to restart your Mac.

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.

Select the Memory tab and see if any processes are using large amounts of memory. I have seen Chrome use over 2 GB at times and increasing, and have had to close tabs on bad sites.

The Memory Pressure chart shows whether you have sufficient RAM (green), could maybe use a bit more (orange), or if it desperately needs an memory upgrade (red). Unfortunately, many Macs are not upgradeable, but it depends on the model and older ones are more easily upgraded than new ones.

The Disk tab is much less important if you have a Mac with an SSD because they are many times faster than old hard disk drives. If your Mac has an HDD in though, click the Bytes Written and Bytes Read column headers to sort the apps and see if any are reading or writing excessive amounts of data.

Monitor activity using 'top'

Underneath the pretty interface, macOS has a lot of commands that can be accessed from a Terminal command prompt. They are not easy to use, but some of them can be useful. There is a command called top that works like a text-only version of Activity Monitor.

1. Go to the Utilities folder and run Terminal.
2. In the Terminal window, just type top and to see information similar to that in the Activity Monitor window.
3. Drag the right-hand edge to enlarge the window and see more columns of data.
4. Drag the bottom edge to enlarge the window and see more rows of apps.

At the top it reports the number of processes, the processor load average, physical memory used and unused, disk activity and so on. Below this is a list of processes (apps and things that run in the background), %CPU, TIME (amount of processor time each process has used), MEM (memory used by a process) and so on.

It is live and it updates every second or two. Use the top command to see if bad apps are using too much CPU, memory or other resources. The COMMAND column lists the app and process names. When you have seen enough, press Q to quit and return to the command prompt in the Terminal window.

Here is a more complex example of top usage:

top -o cpu -O +rsize -s 5 -n 30

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 column in descending order
-O +rsize = secondary sort apps by memory usage
-s 5 = update every 5 seconds
-n 30 = show the top 30 processes (increase window size to see them all)

Press Q to quit, then type:

top -o +command -O +rsize -s 5 -n 30

This time we sort by the Command column and the + means reverse the sort (otherwise the biggest would be at the top - Z is bigger than A).

The top command has a lot of powerful features, but it is complicated to use. Press Q to quit if it is still running and then type man top which displays the manual for top. It goes into quite a lot of detail about the command, its usage and many parameters and options. Press Q to quit the manual.

Related: Solve Spotlight indexing problems with Terminal commands

Monitor the system with XRG

XRG is a different type of system monitor and it is non-standard but useful if you want to keep something onscreen as you work to monitor activity. The Activity Monitor window is just too big on MacBooks, but XRG is small enough to keep onscreen. Download XRG, it is free, and unzip it. Drag the the app to the Applications folder and run it.

It has vertical and horizontal views that enable you to put it along the sides, top or bottom of the screen out of the way of your app windows. Drag the left and dright edge to increase the size.

There are a lot of configuration options in the Preferences, including some weird ones like showing weather and stocks graphs. Explore all the options on each of the tabs to get the display just how you like it.

One of the useful features of XRG is that it shows information that is not in Activity Monitor, such as the temperature of components like the CPU and memory. If the Mac feels hot on the outside, imagine how hot it must be inside. No, don't imagine, run XRG and it will tell you in the temperature section.

A high temperature is usually caused by one or more apps working the CPU and/or graphics very hard. Play a game and then check the temperatures with XRG to see the effect they have. That is normal and expected, but when regular apps misbehave because of bugs or being poorly written then it is a problem.

The app was last updated in 2017 and I don't know whether it supports the hardware monitors in the latest Macs. Try it and see.

More activity monitors

TaskExplorer is an alternative to Activity Monitor that is worh checking out. It is not my favourite app and I'm not sure it was fully working when tried it, but see for yourself, it is free.