How much disk space (GB) does Android 5.0 OS take up? Is "System memory" the OS? Is 5.5GB typical? Can I free any of it? I've been a proud owner of an Android for all of ~6 hours now. I just upgraded from my dumb phone, to a smart phone, for the first time ever, this afternoon. I know, a little later than most...  

I have a 16GB Samsung Galaxy S5 from Verizon.
Phone Name: SAMSUNG-SM-G900V
Model Number: SM-G900V
Android Version: 5.0
Kernel Version: 3.4.0
etc etc...  

I put in a 16GB micro SD card, turned it on, configured it, installed a half-dozen apps, took two pictures, moved over all eligible apps to the SD card (via Settings --> Applications --> Application manager --> SD card menu), then I looked at the memory usage.  

Settings --> Storage shows only 7.13GB free on the internal memory, out of 16GB. This seems pretty shocking to me. The only things that stand out are: Applications, 2.45GB (ok, I suppose I understand that...), and "Miscellaneous Files", 5.47GB. Of the Misc. Files, 5.46GB is "System memory."
What exactly is "System memory?" Is this the Android 5.0 OS? Is it normal to be this large? (I would have expected the OS to be more like ~2GB, and certainly &lt; 4GB). Is any of it space I can free up?  

With normal usage, installing another couple dozen apps over the next couple yrs, and trying to store all photos externally on the SD card, do any of you foresee me running out of memory really soon?

Thanks for any insight.

PS. Here is the info exported from the DiskInfo App, per the request in the comments.



 Internal Storage (MMC)


System [mmcblk0p23] (/system) [ext4]
Used: 2.5 GB, Free: 455 MB, Total space: 2.9 GB
Cache [mmcblk0p24] (/cache) [ext4]
Used: 32.6 MB, Free: 991 MB, Total space: 1 GB
Data (userdata) [mmcblk0p26] (/data) [ext4]
Used: 4.6 GB, Free: 5.9 GB, Total space: 10.6 GB


 SD Card


External SD [mmcblk1p1] (/mnt/media_rw/extSdCard, /storage/extSdCard) [vfat]
Used: 204 MB, Free: 14.5 GB, Total space: 14.7 GB


 Memory


RAM
Used: 1.3 GB, Free: 421 MB, Total space: 1.7 GB
Swap
Used: 966 MB, Free: 313 MB, Total space: 1.2 GB
Firelord gave me the tools to answer my own question, by asking me to post a screenshot of DiskInfo, which I have now added below my question. Corrections (if any) to my answer here are welcome.

Looking at my DiskInfo, according to my understanding of Linux, I'll make the following deductions:  

Android 5.0 (ignoring the SD card) consists of the following 4 partitions:
1. mmcblk0p23, for System, 2.9GB
2. mmcblk0p24, for Cache, 1.0GB
3. mmcblk0p26, for Data (userdata, incl Apps), 10.6GB
4. Swap, 1.2GB (equivalent to the Windows "virtual memory" file, for instance)

Partitions 1, 2, and 4 must be what comprise "System Memory," which is what I asked about in my question. Their sum is 2.9 + 1.0 + 1.2 = 5.1GB
My "System Memory" however is 5.46GB. Why the 0.36GB difference?* I'm not exactly sure, but I've answered my question essentially: Android 5.0 is 5.1GB if you use these "default" partition sizes.  

*Answer (thanks to @user1958698 below): Android uses true, base-2 memory size, where 1 GB = 1024^3 = 1073741824 bytes, whereas DiskInfo uses the rounded off base-10 memory size, where 1 GB = 1000000000 bytes. The ratio is 1073741824/1000000000 = 1.074. DiskInfo's sum (base 10) is 5.1, so multiply by 1.074 to get the base-2 equivalent, and we have 5.1 GB x 1.074 = ~5.48 GB, which is almost the same as the 5.46GB of "System memory" reported by the Android Storage settings. Now, the minor discrepancy between 5.46GB and 5.48GB must certainly be due to some rounding error in the initial 5.1GB value reported by DiskInfo.

Can it be shrunk? Sure, you could shrink Swap, and and shrink System by &lt;455mB, but it's prob. not worth it. Shrinking Swap could reduce performance, and shrinking System could require expanding it again the first time there's an upgrade. 

Update, 13 May 2016:

FYI, I've now run out of internal storage memory for apps, and I have cleared all the cache. It turns out the 16GB version of the phone is NOT big enough for my needs. I will now figure out how to get apps to install onto the SD card by default, so I can free up internal space. This will probably require repartitioning the SD card, using gparted on a Linux computer, and/or rooting the phone. We shall see. 

Nevertheless, here is a key piece of information for Android 5.0 users: once you get down to &lt;~600MB free space on internal storage, you will no longer be able to sync gmail, update apps, or install new apps. You will instead consistently get an error that says, "Insufficient storage available." Therefore, ~600MB seems to be the magic amount of free internal storage that must be available for stable operation of the phone. Note: for some small apps, I was able to get down to 200~300MB free and still update them, but to update my bigger apps, like Facebook, gmail, Google Photos, etc, I had to free up to ~640MB or so before they would update.