Palm OS Programming, 2nd Edition

Types of Memory

All Palm devices have two types of memory: read-only memory (ROM) and random access memory (RAM). This may not seem so different from other operating systems, you might be thinking to yourself. Well, there are some unique twists in the Palm OS. Let’s talk about ROM first and then RAM to see how they are used differently.

Read-Only Memory (ROM)

Read-only memory (ROM) contains:

• The operating system

• The built-in applications

• Default databases

This ROM is an actual masked ROM on some devices (for example, Handspring Visor and Palm m100). On most devices, however, this memory is actually Flash RAM, which can be programmatically changed. The fact that Flash can be changed is what allows most devices to be updated with later versions of the OS. In addition, there are third-party applications that allow users to add databases or applications to the Flash. This is normally done to take advantage of unused space in Flash, and to have databases or applications that will be preserved even after a hard reset.

Tip

At this point, there is no official support for adding databases or applications to Flash other than in the Symbol units (the Symbol SDK has a utility for creating ROM images that includes specific databases and applications).

Most devices have 2 MB ROM, although original PalmPilots had as little as 512 KB ROM. Adding items to Flash works best with units like Symbol’s, which can be obtained with as much as 4 MB ROM. Such luxurious amounts leave plenty of room for adding ...