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The System Information app popped-up today telling my disk is nearly full (65 gigs of 256 gig drive).

➥ That tool reports that "System" is taking 132 gigs. What exactly do they mean by "System", and why is it so large?

I find it hard to believe that macOS Mojave 10.14.6 is itself so large as to take more than half the smallest size drive that Apple ships. Not so long ago Apple was shipping Macs with 128-gig drives.

The Activity Monitor app reports "Swap used" as 3.8 gigs. But that still leaves 128-gigs as inexplicably bloated.

My Question is similar to What is 'System' on mac laptop storage?. But the accepted Answer there is weak and seemingly incorrect.

(I won't even bother asking what is "Music Creation" and why is it 2 gigs when I don't create music.)

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    System is just things that don’t fall into other categories. What are you trying to do or is this purely a why is this happening post? (I won’t even bother posting an answer but you can clean up storage using this tool if you you wanted. )
    – bmike
    Dec 11, 2020 at 22:41
  • @bmike I showed a screenshot of that tool in the Question. I don’t see how any of those options would impact “System”. And those options would do little for me to free up storage space as you can see on that screenshot how little I have stored on this Mac. Dec 11, 2020 at 23:41
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    "Music Creation" may be the Garage Band support files. Instruments and the like. When GB first came out I was amazed at how much stuff it stored in Application Data. If you never use it it is safe to delete. Dec 11, 2020 at 23:54
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    You can also boot into Safe mode, which will delete all font caches, kernel caches, and system caches. These caches can grow over time, sometimes to absurd sizes, and can be expunged without consequence.
    – IconDaemon
    Dec 12, 2020 at 0:38
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    Wonderful news @Pedro - I’ve added that cleanup link to my proper answer in hopes it helps everyone.
    – bmike
    Dec 12, 2020 at 12:30

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System is everything on the disk that takes up space and does not fall under other named categories. Unless you have a spotlight issue or the system is still indexing, I would use a tool like Daisy Disk to get a second opinion on system. Have seen it where a category doesn’t finish indexing so perhaps you have 80 GB of documents, but the indexer crashed at 80 MB and system looks bloated when it’s not.

While that’s running, be sure to take advantage of all the Apple steps to clean things you don’t need: https://support.apple.com/en-us/HT206996

If system remains larger than you like, back up and do an erase install. When you log in, you convince yourself the system is not bloated, but the things you've brought to the Mac are what use the disk space. After that, migrate your data or import things again.

To save a double erase, here are sizes of a survey of system sizing per system after importing apps and setting up users and using them for a week to a month:

  • Mojave: 23.17 GB
  • Catalina: 11.31 GB
  • Big Sur: 14.95 GB (M1 with Rosetta)

After an erase install, you should be even slimmer on the system sizes than listed above.

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