Check out the new USENIX Web site. next up previous
Next: Automation of Persistence Up: The Palm Connected Organizer Previous: The Device


The Operating System

PalmOS is a simple, single-tasking operating system with a GUI widget set that enables the application developer to build event driven, graphical applications.

The 2 to 8 MB of physical RAM is divided into two parts:

This partitioning of the device's physical memory can be avoided by using the undocumented system calls MemSemaphoreReserve/MemSemaphoreRelease. These will switch the memory protection of the ``static'' memory area off and on. When these calls are used, great care has to be taken when issuing other system calls as some may need the semaphore. This forces the programmer to release the memory semaphore before entering certain system calls.

As mentioned in the introduction, PalmOS has no automatic multi-tasking capabilities. If a user changes from one application to another, the first one will be asked to stop by an AppStop event. Once it has stopped, all dynamic memory will be reclaimed by the operating system. The second application will then be started using the same dynamic memory as the first. The operating system does not provide any implicit support for saving the context of an executing application. Instead, the application programmer is forced to save the state explicitly, in a database residing in static memory.


next up previous
Next: Automation of Persistence Up: The Palm Connected Organizer Previous: The Device

2001-02-27