We recently received an email from iPhone Atlas reader Larry who wrote:
"How much memory should someone leave free on the iPhone for it to function properly? [...] In my case, I added a movie to my iPhone leaving 600 mb left on an 8 gb iPhone. While the iPhone worked properly, I started noticing behavior such as the home screen stuttering when returning to it (pressing the home button, the iPhone started returning to the home screen, stopped, then again went through the animation of widgets returning to the screen). I deleted the movie and this behavior stopped. Perhaps that's a coincidence, but I took it as an indication that I was approaching the limit of how much I could put on my iPhone without affecting it."
It's no coincidence, Larry. As we noted in mid-July, it appears that, like its desktop relative Mac OS X, the iPhone's OS X operating system needs some head-room on the internal flash memory in order to operate properly. iPhones filled to the brim with data can exhibit issues with crashes in applications, freezes and others.
The desktop version of Mac OS X requires at least 10 percent of the volume it is contained on as free space in order to maintain the integrity of the file system. However, even with 10 percent free space, Mac OS X's use swap files - as well as extra data generated by third-party application caches, etc. - can quickly put you back into a position of possible directory/file damage.
We're not sure yet how exactly the iPhone's OS X filesystem works relative to the full-blown version of Mac OS X, but for if you're experiencing repeated problems similar to those aforementioned, try clearing up about 10 percent of its free space (by reducing the number of files/data synced to the device in iTunes) and check for alleviation.