Memory expansion
From TreoCentral
All Treos created after the Treo 300 include a card slot that can be used for memory expansion. SD cards (or the rarer MMC cards) will work in the Treo.
No Treo is able to run programs directly off of cards, instead they are copied to the Treo's RAM (much like how it works on a typical desktop system). However, it is generally a good idea to keep as much RAM open as possible to maximize stability - thus the original need for memory expansion in PalmOS devices.
These days, however, memory expansion's main utility is often holding multimedia files such as photos, mp3 audio files, or videos.
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Where to Buy
Memory cards can be found in the TreoCentral Store
