After months of trying to figure out why my phone is slowing down, I just randomly discovered that deleting a bunch of data from the internal memory storage causes it to run fast no matter what apps I’ve got on the phone or what’s on the removable microSD card.
While I do have an old phone (for now), this may apply to current phones, and I do believe in keeping them alive as long as I can and I still utilize every device I’ve retired (jukeboxes, video/game players, backup phones, whatever), so hopefully this will be helpful to you or users like that.
I use a Motorola Droid RAZR MAXX and the Android Assistant app to back up the apps before I update any of them just in case the newest version sucks (more often than I’d expect). When I was running low on memory, I moved them to my laptop, and low and behold, the phone started running faster! I added other content along with continuing the backups over time, and my phone starts running slow again (this was also after several app installs, most of which go to the SD card). Because I had added different things, deleting those apps didn’t speed it up quite as much again, and since I wasn’t sure which was the problem, I just factory reset the phone and deleted all internal storage. It ran fast again of course so I experimented with installing apps.
After all the experimentation, the only thing that consistently keeps the phone running fast is keeping the internal storage usage low. The internal memory is not RAM (of which my phone has 1GB), and it is not the SD card, it is pre-installed non-removable flash memory where app data is saved. I only store music and camera stuff on the SD card, and the phone’s behavior did not change no matter what I had on there. It is still running fast even with multiple anti-malware scanners on it.
I really can’t explain how keeping the internal storage down causes the phone to run fast, but it may be because of the way the file system is scanned or its index (folder/file map) is stored in RAM and is being constantly inefficiently (maybe necessarily) scanned. There is a quirk in flash memory where deleting data can slow down access times, but I wasn’t constantly doing that. In Android 4.3, Google added an optimization called TRIM which frees up deleted data (that gets technical and I won’t explain it here), but that’s not available on my 4.1.2 phone (which is the final update for it).
If it’s not that, then Motorola just programmed the phone very inefficiently, and I have no way to test that, but I can say that I haven’t noticed speed decreases with more data usage on my Galaxy Tab and Droid 2, which also have their own internal storage, but I don’t use a high percentage of data on them (most of it goes to the SD card).
In case you are having this issue, check that you are running Android 4.3 or above, and if not, delete as much as you can from the internal storage (check the online guides for this and make sure you’re deleting extraneous data in the right memory location), and see how the performance is.