iMac Slow? 7 Ways to Speed up iMac & Improve Performance

Last updated: Apr. 23, 2018

iMac running slow

Over time, an iMac (or any Mac computer) can slow down for many reasons.

Cluttered hard drive, loaded login items and launch agents, too many applications running the background, even macOS itself (e.g. latest 10.13 High Sierra) can be the possible causes.

Slow iMac performance may be caused by inadequate hardware too, for example, the internal hard drive is aging and under-performing, not enough RAM (random access memory) to process large app request, etc.

When an iMac slows down, our work productivity tends to decrease because of the emotional consequences. Scientific study shows that frustration caused by a slow computer affects our health, shocking right?

That's why we put together this article -- sharing a list of actionable tips that help speed up an iMac ​and by implementing some of them you can make your iMac fast again.

1. Optimize iMac Startup

If your iMac takes more than 30 seconds to fully boot up and reach the desktop screen, chances are you're having too many login items, or launch agents (app services that auto-run in the background). In other words, there might be too many third-party apps or services opening up once you press the start button on the back of your iMac. When the list of login items add up, it's not surprising that your iMac will slow down.

Fortunately, disabling unnecessary login items is an easy task. Simply click on the Apple logo on top left of the main screen, click System Preferences > User & Groups > Login Items. Here, you can select any items you don't want and click the minus sign "-" to disable them. This video shows you how:

On the other hand, those sneaky "launch agents" may have been added to your startup as well. Unfortunately, it's not easy to disable them via the above technique because they are often not shown in the Login Items list. But, you can use an app like CleanMyMac to easily locate and remove them. 

Simply download CleanMyMac 3 on your iMac, install and open the app. Under "Extensions", find the "Launch Agents" feature and here you're able to disable or enable any helper applications or services. By the way, you can manage Login Items there too.

2. Close Programs Running in the Background

For some applications, even if you have clicked the red "x" sign located on the upper left corner, they may be still running in the background. If you have too many such processes running at once, your iMac speed can be significantly affected, worse yet, the whole Mac freezes up to death. And you'll have to force quit apps or have a hard reboot.

To see what apps and services are consuming lots of system resources (CPU, memory, battery, etc.), use the Activity Monitor app (or iStat Menus) to find them out. Apple has a support article on how to properly use this utility. See this video for more:

3. Clean up iMac Hard Drive

All Macs will run slowly once the startup disk is almost full. Some macOS features or utilities might even malfunction under low storage. Also, lack of free space is often a cause of more frequent hangs, freezes, and app crashes.

To move more space on your iMac hard drive, your first step is to get an overview of the storage. To do so, click on the Apple icon, then About This Mac. Under the Storage section, you can see how much space is available on current disk. Different blocks of color indicate different file types, such as movies, photos, or apps.

Then, clean those unnecessary files such as system junks, unused apps, large old items, etc. Again, CleanMyMac is a time-saver, it helps you determine what specific files are taking up the most space and indicate which are safe for removal or transfer.

Meanwhile, you can also use Gemini 2 to quickly get rid of those duplicate and similar files (especially photos). Both CleanMyMac and Gemini are designed and developed by the same company, MacPaw.

4. Run the Right macOS Version

Depending on the iMac model you are using, you may want to double check whether the macOS version your iMac runs is the best option. For example, the latest High Sierra does not always guarantee better performance, especially it requires at least 2GB of memory and 14.3GB of storage space to perform the upgrade.

If your the hardware configuration of your iMac is a bit behind, chances are it'll run slowly after the update. In fact, many iMac users reported the issue.

So, know your iMac and run the right macOS. To check what macOS version your iMac is with, click Apple logo > About This Mac, there you'll see the information. Then you can choose to upgrade to a newer macOS or downgrade to a lower one. 

5. Remove Unwanted Programs and Extensions

How many times have you downloaded an app or browser plugin, but only used it for once and later you totally forgot its existence?

Days and months later, you may surprisingly find that your iMac is filled up with such unneeded apps/extensions. Most of them won't do any harm except taking some storage, some may run quietly when you start up your Mac or while you surf the Internet via Safari, Chrome, Firefox, etc.

So, it's always a good idea to remove such unneeded apps and plugins to give your iMac a little bit performance boost.

The easiest way to start with is go to the Applications folder, drag and drop those unwanted apps to trash and empty Trash.

To Clean up browser plugins/extensions, open the settings of your browser and you should be able to find the right place to manage those extensions. For example, I'm using Chrome (ver. 64 for Mac), just click the three-dot icon, then More Tools, and find Extensions. There I can see all installed plugins, and choose to delete or disable those unwanted.​

6. Add More RAM

RAM (random access memory) plays an important role in processing app requests. If you are a designer or developer who uses an old iMac for video or photo editing projects, chances are RAM may be the bottleneck. When RAM is used up, your iMac has to switch to use disk virtual memory which will ultimately lead to slow iMac performance.

The solution? Consider adding extra memory!If you decide to do so, be sure to check how many GBs your iMac is able to add from this Apple resource. For example, most 27-inch models, the base memory is 8GB and you can add up to 32GB.

For RAM upgrade options, consider Crucial 16GB Kit (8GBx2) and OWC 32GB for 2017 iMac 27-inch with Retina 5K display.

Also, don't forget to check out this video before opening your iMac mainframe to install additional RAM. 

7. Upgrade to an SSD

For older iMacs, replacing the current hard drive or fusion drive with an SSD (solid state drive) can significantly improve your Mac's speed and performance. Similar to adding more RAM, be sure to check which SSDs are compatible with your iMac model.

For iMac SSD options, consider this OWC SSD ​Upgrade Bundle if you're using a 2012-2015 iMac or OWC Mercury Electra you're on a 2011 mode iMac.

This video shows everything you need to during the process of replacement.

That's all that we wanted to share out with you. Hope you like this iMac performance troubleshooting guide. Kindly let us know which way(s) you find most useful in speeding up your iMac? We're here to hear from you.

Andreas is an Apple and Microsoft fanboy who works with his Mac and lives with a PC at home. While he is not reading technology journals, you’ll probably find him playing online games with friends or hiking in the wild.

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