When you update to iOS 10.3 on your Apple device, you are going to have Apple's new file system (APFS) installed. Will you notice, or even care? To learn more about what and why Apple is doing this, here is an article worth reading.
I've done the update on my iPhone and iPad, and did notice the install process took longer than usual. I didn't give it much thought at the time, but, after reading the article, I now realize a lot was going on. It's difficult to comprehend all those 0's and 1's being switched around to a new file system, and still working correctly afterwards.
Congrats to Apple's Engineers. Next up for conversion to APFS will be our Macs.