Types of system RAM in Linux/macOS

RAM moduleAnother article for beginners. If you know what RAM means, you can skip this introducing part and go to article directly. If you can’t imagine how RAM works, I will try to explain it by example. RAM – Random Access Memory – is one of key hardware component of our computers. It’s something like temporary memory. Just imagine it: we are at school at History lesson. We are hearing teacher and taking notes. We have notes in our sheet – this is harddisk – and in our actual memory – this is RAM. After History is coming another lesson – Geography. We are again hearing teacher and taking notes. But our brain memory capacity is limited and some facts from History we have forgotten, but they are still in our “harddisk” – sheet. So, theoretically, we can say that all lessons in our sheets are something like harddisk in computer and school datas, we are actually using, are RAM. We may forget something, because of limited capacity of “RAM” in our brains, but we can still regain data from sheet – harddisk. We can’t use all data we learned in whole life at the same time (“low RAM memory”), but we can regain our data from sheet, but purging some other datas from “RAM” in process. Data in sheet are unaffected and can be regained into our “RAM” at any time, if we forget something and we need it. This is how RAM memory in our computers works. More RAM means more data we can use at the same time.

Now article itself.

In Windows operating system are two types of RAM – used and free. In UNIX-like systems, like macOS and Linux distributions, it’s little more complicated, as these operating systems feature advanced management of RAM. We can see these types of RAM:

  • wired
  • active
  • inactive
  • free
  • compressed (OS X/macOS only)

So now let’s look how it works:

Wired: this is amount of RAM accessed directly by operating system itself. No other apps or processes are allowed to access it. It helps to increase security and stability of operating system.

Active: this is active used RAM by your opened apps, documents, multimedia, processes in background etc.

Inactive: this is little complicated. Inactive RAM is something like cache (like cookies in your Internet browser). If you have closed some app recently, you can reopen it faster, because some “parts of app” are still stored in RAM. If you are getting out of free RAM, this cache is being cleared.

Free: free memory, which is not used by any apps or operating system itself. As it name says – it’s really free memory, which can be used later, if required.

Compressed: this is RAM management feature included in operating system created by Apple – macOS (formerly OS X). It’s available since OS X 10.9 Mavericks. As we can compress files into RAR / ZIP archive to save space, we can do it with Inactive RAM (cache) too. This process is fully automated by operating system itself.

Sometimes we can see something like “GPU allocated memory”. Integrated graphics cards use system RAM, because they don’t have theirs own dedicated memory, like discrete/dedicated graphics do. This is reason, why some games need 8 GB of RAM under Intel HD 4400 graphics, while if you have discrete graphics card, 4 GB of RAM is enough. But some hi-end integrated graphics cards, like Intel Iris Pro, got some own dedicated memory.

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