How does memory work on a Mac and how much do you need?

December 6, 2021 | Reading time 7 minutes

Recently, I bought a new MacBook Pro with the M1 Pro chip. I went with the base model of the 16″. One of the reasons to go with the big MacBook Pro was that I wanted the bigger screen —I’m not a fan of external monitors— and this one is gorgeous. I doubted about the amount of RAM, but the € 469 that Apple charges for 16 GB of additional memory is ridiculous. —Side note: at the time I also looked and the Alienware X17 and Dell only charged € 20 for expanding the RAM with 16 GB.—

That price brought me to the questions how much memory is required for my workflow and how does memory work on a Mac?

My old MacBook Pro gave the easy answer. It also has 16 GB of memory and that was sufficient during the time it was my main machine. But, it did not answer how memory on a Mac works. Instead, it raised questions. For example, at one point I looked at the activity monitor, and it said 10 GB of memory in use and 5 GB of cached files. The only apps I had open were Notes, Safari with four tabs, finder with two tabs and iA Writer. And after opening apps like Affinity Designer and Visual Sutdio Code, it remained at 10 GB.

So, why was there 10 GB of memory in use? After some research, I found out that macOS uses as much memory as available for speeding things up. This was great, but it made it difficult for deciding if the 16 GB was enough for my future needs. Most of my work consists of using Safari, Chrome for web development, Visual Studio Code, Notes, OneNote, Microsoft Remote Desktop and a Markdown editor. And the memory hog Microsoft Teams. I guessed 16 GB would be enough.

At this point, I could just follow my sense or do more research. I chose the latter and took a closer look at Activity Monitor.

Checking memory in Activity Monitor

On macOS Activity Monitory is the utility tool force quitting apps, checking energy consumption of your Mac and apps, and check CPU and memory usage.

A screenshot of the Activity Monitor app in macOS with normal use.
A screenshot of the Activity Monitor app in macOS with normal use.

We want to focus on the following items in the Memory tab:

  • Memory Pressure.
  • Physical Memory.
  • Memory Used.
  • Cached Files.
  • SWAP.

Physical Memory

The Physical Memory is on a hardware level and is the amount of RAM on your device. In the past, you could upgrade RAM yourself, but these days that is not an option anymore on MacBooks. That is one of the reasons why I like Windows gaming laptops. You can still upgrade those devices yourself.

Memory used

Memory Used is split in App Memory (memory used by apps), Wired Memory (memory used by macOS) and Compressed Memory. The latter is the amount of memory that your Mac has compressed to make more RAM available.

Apple’s website says that memory compressing occurs when your computer approaches its maximum memory capacity. Your Mac compresses inactive apps in memory, making more memory available to active apps. I don’t think this is entirely true. Yes, macOS compresses memory to free memory for active apps. But, it does not only occur when your Mac is running low on memory. I notice it after a reboot too when the only apps open are Notes, Finder, Safari with five tabs open and iA Writer.

It seems to me that macOS compresses memory as soon as it can. This way, the system maximises memory for cached files and active apps.

Cached files

The system caches files into unused memory to improve performance. Cached files help improve performance when you reopen an app. It remains cached until this memory is overwritten.

SWAP

When your Mac runs out of memory, it copies data between RAM and special files on your startup disk. This is known as swap files. It gives the appearance of the system having more RAM than is physically installed.

With the first M1 Macs, it seemed that macOS was swapping quite aggressively. Apple fixed that in an update, and I don’t see much swapping on my MacBooks. Let alone large quantities.

But how do I know if my Mac needs more RAM?

Activity monitor has one more important item for checking the use of memory: Memory Pressure. This is perhaps the best way to check if your workflow requires a Mac with more RAM.

Memory Pressure shows how efficiently your memory is handling your processing needs. Activity Monitor has a small graph that reflects it. The graph has three color options that it shows for memory pressure:

  • Green: RAM works like it is supposed to and performs at its best.
  • Yellow: RAM works fine most of the time, but your Mac might eventually need more RAM.
  • Red: your Mac needs more RAM. AKA: go throw your money at Apple.

Of course, you need to look at how yellow and red memory pressure occur. It depends on the work you do and I did a few tests.

For my testing, I tried to push my MacBook in different scenarios that apply to me. In most cases, memory pressure stayed in the green. It never went red and only turned yellow while running these apps at the same time:

  • Visual Studio code.
  • Blender with a 490 MB file.
  • Affinity Designer with two files and many layers.
  • Affinity Photo with a 68 MB file.
  • Sketch with one file.
  • Notes.
  • OneNote.
  • Safari with twelve tabs.
  • Chrome with three tabs.
  • Microsof Remote Desktop.
  • Microsoft Teams.
  • WhatsApp.
  • Typora.
  • Nota.
  • Finder with four tabs.

This is an unlikely scenario for me, but nonetheless was a good test. Apps like Blender and Affinity Photo use a lot of memory, and I barely use them. More importantly, even in this unlikely scenario, my MacBook Pro —with M1 Pro chip— performed like it always does.

A screenshot of the Activity Monitor app in macOS while pushing memory usage.
A screenshot of the Activity Monitor app in macOS while pushing memory usage.

A side note for Microsoft Teams. As of writing, the app is not yet optimised for Apple Silicon and this might lead to higher memory usage. On first launch after a reboot it uses 800 MB of memory on my Intel Mac and 1.3 GB on the M1 Pro. Perhaps the latter will improve when Teams becomes Apple Silicon native.

Free up memory before buying a new Mac

The way you work also impacts memory pressure. I used to open apps and leave them there forever. And I collected open tabs in Safari and Chrome like it was money. This habit leads to unnecessary memory usage.

These days, I close tabs in Safari or place them in a Tab Group. —Apple introduced Tab Groups in Safari 15. It helps me manage tabs and in addition, it frees up memory.— The same goes for closing apps. Together, it reduced my average memory pressure with at least 20%.

Conclusion

How much memory does your MacBook need? The answer is not straightforward and depends on your workflow and your computer habits. If you frequently work with 3D software like Blender or compile code, you might want 32 GB RAM or more. In most other cases, 16 GB will do the job for most people. I stick with 16 GB for this machine.

p.s. If I made wrong assumptions, please let me know (hello@wimpostma.com).

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