Is it normal that "system" takes up 36 gb of storage? What does is contain? Can it be decreased?

Have a look at this thread, might give you some answers - from what others have posted your 36Gb could be quite small by comparison.

Why does the system use 150 GB of storage?

A clean installed Sierra fits into around 14GB for me (that is everything). The 'system' is around 9GB of that.

When you upgrade you leave all the third party application data in place - this may include caches & other supporting files. You may or may not need those it really depends on what apps you use and how old and relevant the data is.

You can decrease the size by removing files you no longer need but it can easily cause problems.

I suggest you look at the advice on managing 'other' storage…

What is "Other" and What Can I Do About It?

OmniDiskSweeper or the other apps mentioned there can help you see where space is used.

Please post here if you are unsure about removing anything - you can break apps or the OS by deleting the wrong things in the System. Also backup first!

Are we talking about the right "System"? On my setup if I go to "About This Mac" then select "Storage" then "Manage" the size for "System" is given as 83.96Gb.

But if I right click on the "System" folder under Macintosh HD and choose "Get info" it is only 7.87Gb (the "Library" folder just above is 4.88Gb and "Applications" folder above that 8.01Gb). The largest folder is "Users" which comes to 78.18Gb.

So for me to reduce the 83.96Gb figure as reported by "About This Mac" by any meaningful amount it would require deleting files from within the "User" folder which just happens to store my music, photos, mail etc as well as caches as pointed out by Drew.

What I'm trying to say is just because "On This Mac" reports a certain "System" size it does not mean that is what the actual operating system is taking, that figure is given by /System and /Library (in my case 7.87Gb plus 4.88Gb) which is approx 13Gb, a far cry from the above 83.96Gb figure.

If I'm looking at this correctly then the easiest way for me to reduce the 83.96Gb figure would be to off load music and photos to external storage, but that would make no difference to the 13Gb figure which is purely OS related.

I would not worry about what that bar graph indicates. It's not indication what's in the System folder but many associated files. My system by that graph is 88 GB in size.

But if you check the Info pane for the System folder via the Finder you get 8 GB.

My recommendation is to ignore that bar graph as it can be greatly erroneous or misleading at times.

Agree totally with your comment to ignore bar graph - that's my whole point, I think people are looking at this graph and starting to panic thinking there "System" has suddenly ballooned in size. In fact the bar graph "System" is recording completely different data and looks as though it also reflects what the user has stored on his machine (personal files) that reside outside what we traditionally used to know as the "System" area.

Hi,

I have also this problem since the latest update 10.12.1. My system tab takes 46 Go (I suppose this is System + Music for me, because Music tab is missing in the graph).

I reindexed Spotlight and repair Disk, no change...

That tells you nothing about how much your system actually uses, it's just a pretty bar graph to wile away the time looking at, if you really want to know look in finder.

Yes, I know that this graph means nothing important... I posted this feedback only because this is the first time that I don't understand how to allow this graph to show properly the disk space sort by category.

Re-index Spotlight, but it will still be inaccurate in many cases.

Already done, and also Disk Repair Utility help... but no change.

Maybe corrected in the 10.12.2 update (I don't participate to the beta test, so I don't know about this).

Wait & see...

Wait and see what?

It is not accurate or explanatory, it is unlikely ever to be either of those things, it was designed for people who want something simple to look at primarily.

Of course it's a simple graph... but really, this kind of issue should not exist anymore. It's not complicate to read the good System file size and plot the given value in this 'beautiful graph bar' (and the same for the others sections like Music, etc...).

It's up to you if you want to take the easy way, you already know what you will lose.

I know how to get the good informations about space disk... the question is not here.