My Apple Mac is slow, does it need more memory?

Some people have found that after upgrading to the latest version of macOS on their Apple Mac, it runs more slowly than it used to. Why does this happen and what can you do about it?

One of the reasons for this could be that the Mac is running short of memory for apps. Old Macs had 4 GB of RAM and if you still use an old Mac you will have noticed that it sometimes slows down. It could be because the CPU is under a heavy load, but that may not be and the problem could be that the Mac is running out of memory.

New Macs have 8 GB of memory, but even though the minimum has doubled, macOS and applications require a lot more memory than they used to a few years back. The Mac can still run out of memory with 8 GB and it just takes a few more browser tabs or open applications.

macOS memory usage

A quick look at Activity Monitor can reveal why the Mac is running slowly or slower than usual, and it can be used to view the CPU activity and memory usage. Let's take a look at the Memory tab when the Mac is running normally. I'll use an old Mac with 4 GB of RAM, but problems can occur with 8 or 16 GB of RAM.

Take a look at the screen shot below, which is Activity Monitor running on an old MacBook with 4 GB of memory. The table at the bottom is the important part and it shows the memory usage. On the left side it clearly says that there is 4 GB of physical memory and that 2.79 GB is Memory Used.

On the right-hand side it shows how the memory is being used, for example, it shows that apps are using 1.75 GB. Some of the other figures are not so clear unless you know how to interpret them.

App Memory is the amount of memory that is being used by applications that are running.

Wired Memory is memory that is currently in use and cannot be used by apps or swapped to disk

Compressed is memory that has been compressed. Just as you would compress files into a zip archive to shrink the file size, macOS can compress memory so that it occupies less space.

Swap Used is memory that has been written to disk (actually Solid State Drive, SSD, these days). Swapping blocks of memory to disk is a way of freeing up memory for running more apps.

The amount of memory currently being used is the sum of App Memory, Wired Memory and compressed memory.

Cached Files you can think of as the free memory. When you run an app, it is loaded into memory from the disk drive. If you quit the app, it stops running, but it stays in memory. If you run the app again it doesn’t need to be loaded from the disk drive and it can simply be activated in memory again.

The file cache can contain more than one inactive app and with a gigabyte or more to play around with, OS X can hold several apps in memory just in case you want to use them again. How many times a day do you check your email? Some apps are run frequently and so it makes sense to store them in memory.

Is your Mac short of memory?

There is a chart in the table at the bottom of Activity Monitor and it is green in the screenshot above. This is good and green means that there is plenty of memory for running apps. Lots of from memory enables the Mac to run at full speed.

If you see yellow/amber sections in the chart, it means that macOS is beginning to run out of memory. If you see a lot of red then it means that macOS is seriously short of memory and it is running more slowly than usual.

To get this screenshot I simply opened 10 browser tabs in Chrome. It deends on the website and some use more than others, and the ones I opened are particularly memory-hungry.

Here you can see that the memory pressure is red and that's bad. The Swap Used has risen from 1.5 MB ro 215 MB and this means that chunks of memory are being temporarily stored on the disk. An SSD is between 10 and 20 times slower than RAM to access and so when memory is written to the swap file, the Mac slows down by a factor of 10 to 20 times.

More memory is being compressed and it is up from 177 MB to 1.43 GB. It takes processing power to compress and decomrpess memory and this will reduce the speed with which it can be accessed. Using a lot of compressed memory slows down the Mac.

The Mac is suffering a double speed hit here, the swap file and the compressed memory. It is why this Mac is running very slowly. When your Mac runs slowly, check the memory usage in Activity Monitor.

Related: Do you need a memory cleaner and are they helpful?

Solve memory problems on the Mac

Some Macs, mostly old ones, can have the memory upgraded. In recent years Apple has been soldering memory to the motherboard and so it cannot be upgraded. Your Mac is mostl likely stuck with the memory it has with no option to increase it.

There are a couple of things you can do and one is to make sure you buy a Mac with lots of memory the next time you replace it. Don't think about how much RAM you need today, think about how much you might need in a couple of years. Plan for the future where macOS and applications will be much larger and require more memory. In fact, it is a good idea to max out the RAM when buying a new Mac. It adds to the price, but the Mac will be usable for many more years.

If your Mac is not due for replacement, the only options are to run fewer apps at the same time and to use lightweight apps. Run only one or two apps at once and quit one before opening another. Don't open so many tabs, such as in web browsers, and don't open multiple documents in word processors or multiple photos in a photo editor. Work on one app and document/tab/image at a time.

Some apps use less memory than others and Safari for example, uses less than Chrome. A Mac will run into memory problems faster with Chrome and it took about 10 tabs on a 4 GB MacBook. Using Safari it took more like 12 or 13 tabs before the memory pressure chart began to turn red.

Use TextEdit instead of Pages for example, because it is super lightweight and uses little memory, and OneDrive uses less memory than Google Drive (it's called Backup and Sync these days). There are sometimes other alternative apps you can use to reduce memory usage.

Don't forget to check System Preferences > Users & Groups > Login Items to make sure nothing is loading and running in the background when you log in.