Mike Calligaro from the Microsoft Windows Mobile team posted an entry on the team blog abou the move from RAM to flash memory use on Windows Mobile 5.0 devices.
The explanation is very interesting and helps us understand why the current Pocket PC models have such a short (in terms) battery life and how moving from RAM to flash memory (Persistent Storage) will change this.
According to the post "A typical battery holds 1000mAh of charge. 128M of RAM takes about 500mAh to stay resident for 72 hours. 64M takes about 250. This is why you never saw a 256M WM 2003 device. It would have run for a minute then decided its batteries were critically low.
This is why switching to Persistent Storage can radically improve your battery life. With PS, we removed the 72 hour requirement. We'll let you run your batteries completely dry, because we know your data will still be safe. Right off the bat, that buys you a significant chuck of time. It also means that no one ever has to make a 128M RAM device again. They can fall back to 64M devices, which burn less power, and store the user data in tons and tons of flash. You'll definitely see 128M flash devices. And there's no barrier to keeping you from seeing 256M, 1G, etc devices. That couldn't have been done with RAM."
So, Pocket PC devices running Windows Mobile 5.0 (and using Persistent Storage) will be like Windows Mobile Smartphones: on these devices, low or no battery does not affect the contents of the memory. It means that your device can run out of power but everything will still be there.