- No multitasking. iPhone OS switches apps, exiting on switch.
- Apps only have access to their own data (sandbox). (I think they may have access to some common pooled data though.)
Both of these limitations were part of the original US Robotics PalmPilot OS (PalmOS), and years ago conventional wisdom said Palm desperately needed a multitasking OS. (I would have had a different set of priorities myself; I thought the memory management issues were much more important than the multitasking problems.)
Jobs, during yesterday's presentation, said something like iPhone OS "draws heavily from OS X". DF has hinted the same thing over the past six months -- "inspired by OS X, but not OS X".
We need a name for this OS, maybe TouchOS. There's obviously a lot in common with Tiger 10.4, but the iPhone team did some radical surgery to build the TouchOS. Only they know the basis for these decisions -- hardware limitations, memory limits, security issues, stability, desperation ...
The lack of multitasking suggests TouchOS can't do Spotlight, or any indexing tool -- that requires multitasking. I wonder how many odd functional omissions are related to underlying OS issues. (The lack of task management, I'm convinced, must come from Jobs himself. I suspect he simply hates To Do lists.)
I'm not worried about the multitasking limitations. There's obviously enough available to enable enough functionality to succeed, the similarities to PalmOS 1.0 are really more curious than important.