The name "system data" is misleading. Most likely what you are seeing there is the total size of the system partitions: not just the operating system, system apps and firmware but also any unused space in those partitions. That's not as unreasonable as it sounds, since you cannot use space in those partitions for your apps or data so as far as the user is concerned it is all being used by "system". About 4.5 GB used sounds about right to me though. They never advertise that the storage they quote is the total on the device, and that the operating system etc will use a few GB of that, so this does still catch people out.

Different phones' storage settings describe things in different ways. If you want clarity, there's a very small app in the Play Store called "Storage Truth", written by Scary Alien (one of our moderators). That will show you the sizes of your main partitions and how much space is used/free in each. The /data partition is the space that's available for your apps and data. Or if you run that app, copy to clipboard from the app's options and post the results here then we can confirm the truth.

TL;DR: "system data" is almost certainly the phone's operating system and firmware, and that's why you can't get rid of it.

 

It may be true actually. How much space have you currently got?

Android needs to keep some space free as working storage (for temporarily caching data). So as a protection against running out of space, the OS has a minimum free storage, and if you have less than that available it won't install any new apps no matter how small. What that minimum is depends on the phone and software version, but on a recent phone it's likely to be 500 MB or maybe more.

 

That's the problem then. Sounds like it needs about 400MB free before it will install anything.

But I've just done a quick web search, and it seems that out of the box only 3.4GB of storage is available on this device. So that confirms my suspicion that these 4.56 GB of "system data" really are the system storage partitions, and hence not something you can reduce.

The real question is, what's using the remaining 3GB of the little space this phone does allow you? Moving apps to SD only actually moves part of the app, and data stored by apps may still be on internal storage even if the app is moved to SD. Go to Settings > Apps, sort by size, and see which apps are using most space. You can free some space temporarily by clearing caches (which is harmless), but clearing app data is likely to remove stuff that you want.

The other thing to check is where your photos are stored. "/sdcard" is actually internal storage pretending to be SD (using the name /sdcard to avoid breaking old apps), the actual SD card will have a different name (could be "sdcard1" or something else). This is bloody stupid to be honest, but Google were so concerned not to break apps as the way storage was used changed(*) that they've allowed the naming to become a confusing mess. But it's possible that some of the stuff (like photos) might not actually be on SD as a result of this confusion, so I thought I'd best mention it.

(*) My first Android had a whole 147 MB available for apps and their data, and /sdcard really was the sd card. But then manufacturers started adding more storage, and to allow people to use that for media they called part of the internal storage /sdcard and found another name for the real SD card. It's developed further since then, but that is the point where this mess in naming emerged (2011).

 

Try clearing Chrome's cache - there's no way the app itself is anything like that size.

 

That file manager is showing you the total space including SD, so the images & videos might be on SD already. If not, where and what are they, and what app are you trying to use to move them? It may be that you just need a different file manager (one that understands SD permissions in whatever Android version you are running).

Chrome is clearly storing more than bookmarks if it's using > 200 MB of data! That is crazy usage. I've no comparison though, since I don't have Chrome installed on any of my devices. I think that simply clearing data on the phone would probably not clear them from your other devices - more likely they would just sync back onto your phone. Deleting them item by item might remove them from your other devices though.