The handheld has two types of memory. Its operating system and built-in applications are stored in ROM memory, and its additional applications and files are stored in RAM memory.
So that you can easily upgrade, some manufacturers locate your operating system in a socketed ROM module, which you can remove and replace with a new one. Another option is Compact FlashTM memory or Secure Digital or Multimedia Card memory (SD/MMC), which can be erased and reprogrammed with an upgrade.
Palm OS handhelds come with 2MB to 16MB of RAM memory. Pocket PCs ship with 16MB to 64MB of RAM memory. Palm is efficient enough for most users to get by with 8MB of RAM memory. Pocket PC users might need more like 64MB for the elaborate applications. Handhelds don't require near the amount of memory that PCs do. For example, 1 megabyte of memory can store up to 4,000 addresses and 100 email messages on your handheld.