Do you need a memory cleaner and are they helpful?

Do you need a memory optimiser for your Apple Mac? What do they do and are they worth it? This article looks at how they work

Go to the Mac App Store, go to Categories, select Utilities and among the free and paid apps are several memory cleaners. They are very popular apps, but do you really need a memory cleaner? What does it do?

First, you need to understand how the Mac handles memory. All recent versions of macOS and OS X have used similar memory handling for years and not much has changed.

Go to the Applications/Utilities folder and run Activity Monitor. Select the memory tab at the top and down at the bottom of the window is a table containing various figures showing how OS X is using the RAM in your Mac.

Activity Monitor memory usage
This is Yosemite, but macOS Sierra is almost identical

This looks straightforward and in the left column it says that the physical memory is 4.00GB and the memory used is 3.66GB. Subtract one from the other and the amount of free memory is therefore 0.34GB or 340MB.

The Memory Clean utility from the Mac App Store confirms this:

Memory Clean app for OS X

There is a slight difference in MB, but that’s because the memory free has changed a little when I ran Memory Clean.

The problem is that this figure is wrong. Subtracting the memory used from the physical memory does not tell you how much memory is free.

Look at the right-hand side of the table in Activity Monitor. The App memory is the amount of memory used by apps that are running. The Wired Memory figure is also apps and macOS memory usage, (important memory not to be messed with).

Activity Monitor on the Mac

The total memory used is App Memory + Wired Memory, which is 1.59GB + 585.1MB or about 2.18GB. Therefore the amount of free memory is 4.00GB minus 2.18GB, which is 1.82GB. This is significantly different to the amount that Memory Clean claims is free.

The confusion arises because of the way that macOS uses memory. Memory that is not used is simply wasted, so macOS puts it to good use. If you run an app, such as Mail, you will see that the App Memory figure increases and this is because more memory is in use.

If you quit Mail, the App Memory figure goes down as memory usage falls. However, the File Cache figure rises. When macOS has lots of free memory that isn’t being used for anything, it will hang on to apps you have quit just in case you want to run them again.

Some people check their email 10 times a day and if the app is still in memory, macOS can restart it in an instant without having to find and load it off the disk drive.

Apps are cached when nothing else wants to use the memory. Rather than leave it empty and unused, macOS stores recently run apps in it.

This means that you can think of File Cache as free memory. If you run one or more big memory-hungry apps, OS X can abandon one or more items in the File Cache and give it to the new apps being run. Watch what happens when I run a bunch of apps.

Activity Monitor memory usage

Memory Used has increased from 3.66GB to 3.98GB and App Memory has increased from 1.59GB to 2.34GB because more apps are now running. The apps need more memory, so the File Cache is reduced and falls from 1.50GB to 1.10GB.

This is a balancing act that macOS constantly performs, using free memory as File Cache and reducing it as apps need memory, then increasing it when apps quit.

The scrolling Memory Pressure chart in Activity Monitor shows whether you are short of memory. Green is OK, orange is not so good and red is really bad. Notice that it is green in the screen shots, yet Memory Clean has changed to red in the menu bar to alert me that there is just 24.51 MB of memory free.

Memory Clean app for OS X

Memory Clean red alert! Only 23.42 MB free memory! But the green bar in Activity Monitor says that memory usage is fine. Activity Monitor is right and Memory Clean is wrong. The File Cache is 1.10GB, which, remember, is like unused memory. If yet another app is run, macOS simply discards something in the File Cache and uses the memory made free.

One figure in Activity Monitor I haven’t mentioned is Compressed. When macOS gets really short of memory, it compresses bits that haven’t been used for a while. It’s a bit like adding files you don’t use very often to a zip archive, only OS X does it automatically and at lightning speed on the fly.

So is Memory Clean and other memory cleaners (there are many more) actually useful? I am not convinced by what I saw when using the app. It appears to work because the free memory figure that it displays increases, but as pointed out, this figure is not calculated correctly and so is misleading. I would leave macOS to figure out the best way to use memory rather than try to force it to work in some other way.

Memory cleaners can be useful under some cirmumstances, but you can gain in one way and lose in another. Clearing memory either moves apps and data to the disk or compresses it, maybe both. When you need to access those apps and data, it can take longer.

The next app you open will run better, but apps that are already open with run poorer.

If you are the sort of person that leaves their Mac running for weeks at a time, just reboot it every so often.





Yes they are. I once cleaned my 4GB transcend with Stellar Speedup Mac. I was surprised to realise the amount of duplicate data found into them. Upon removing them at-most 1.5Gb of storage was claimed back. I can't imagine to do it manually, yes a free cleaner software would be of great help.

Vishal, the article is about memory cleaners, which I am not convinced are useful. You are talking about disk cleaners, which are definitely useful. Good free disk cleaners include AVG Cleaner for Mac and OnyX. Grab a copy of these and your Mac will be cleaner, leaner and clutter free.

@ rwaddilove Stellar Speedup Mac is also a Mac cleaner software which I used to clean my Mac as well as a spare memory card. I was happy by the result it gave me. I suggest you try this software.

Thanks for the info, I'll put it on my to-do list.

The article is here

Your explanation of the process OS X uses was excellent. Too bad the developers of some of those memory cleaner apps don't include that in their support manuals.

Thought my free memory app was doing a good job till it started with crap about upgrading blah blah.. deleted it and paid $2 for another app which froze and took me 30 mins to figure out how to delete it! Thank you for that awesome explanation on how the mac does it. Won't be downloading these apps again! Thank YOU!

Just wanted to chime in. There are some cases where memory cleaner and others are VERY useful. If you are using media editing or recording software (think Final Cut Pro, Logic, etc...) they can use large amounts of RAM as soon as you execute a rendering or recording command. While OSX does manually manage the File Cache memory well, it is not always fast enough to do it before the app makes a huge demand on the resource and can crash or freeze up the app. I typically only use it for this reason. Just before recording or rendering I tell it to clean the memory, which empties the file cache and prevents my Final Cut or Logic from crashing or freezing. SO, you are right in that most people don't need memory cleaners, but there are cases where it can be very useful.

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