I was recently asked about the difference between active, inactive, and wired memory on computers. Many memory measure tools use these terms to describe your memory usage and doesn’t really go into much depth about what they mean.
In this piece, I hope to shed some light on this confusion and explain the differences between these memory states the best I can.
The Activity Monitor app that ships with the most recent releases of macOS shows memory in three forms: “App Memory,” “Wired Memory,” and “Compressed.” Apple has certainly gone a long way in dumbing-down their hardware monitoring software from past macOS releases, but the three main states of memory still exist as a part of your system.
To simplify things, I’ll compare memory to a bank account. You’ll see why in my breakdown below:
Active memory is your computer storing data that’s being accessed by your running apps. Storage disks are too slow to act as memory and that’s why your computer stores this information inside your memory.
In terms of a bank account, compare active memory to the withdrawals and deposits that are going in and coming out of your bank account, such as those from direct deposit and automatic bill pay. These happen in real time and in a very short amount of time.
When you see a chunk of your computer’s RAM being labeled as “Active,” it just means an app(s) is using it. You could free it up if you needed to by closing some of the apps you have running.
Wired memory can’t be written to a storage disk because it needs to be ready as soon as you turn your Mac on. Wired memory is where your computer stores important background information, such as what’s related to your kernel, software, and other core functions in your operating system.
Once again going back to the bank account analogy, wired memory can be compared to the required minimum bank deposit you have to keep in the bank to keep your account open. This is the money you can’t withdraw because it keeps your account running.
Because the core processes of your operating system that manage apps on your Mac are stored here, you might see this amount fluctuate as you open and close apps on your Mac, but there’s no way to really free this memory because it keeps your computer running.
Inactive memory is exactly what it sounds like: memory that isn’t being used. If you have a machine that has a lot of RAM, you might see a lot more inactive memory because it gets harder to fill all of it. If you have very little inactive memory, then you might need to consider a RAM upgrade in the near future.
The final piece to my bank account analogy refers to inactive memory; this can be compared to the money in your bank account that you aren’t using, excluding the minimum bank deposit required to keep the account open.
Another beast: compressed memory
Beginning with OS X Mavericks, Apple introduced compressed memory. This is another form of memory that you need to understand because it allows you to do more at once with less RAM.
Essentially, compressed memory is an attempt to reduce the chance that your RAM will bottleneck your machine. Compressed memory is essentially stored information that has been reduced in size so more information can be stored in a limited RAM scenario.
Think of this like a compressed ZIP file: you are essentially packaging everything up into a folder and might end up with a smaller file size than expected. When you need it again, you un-zip it and get all the contents back out. This is the case with compressed memory too, as the computer can just uncompress it when it’s ready to use it.