Since the launch of the original iPhone, Apple has made efforts to hide some of the actual tech specs of the device from consumers. Apple has never advertised or even published the processor speed or amount of RAM found in the iPhone. Arguably, Apple is trying to shield customers from these technical distractions and instead trying to focus on overall functionality.
More technically inclined customers, however, still love to know what they have to work with. The original iPhone and iPhone 3G contained 128MB of RAM, while the iPhone 3GS was boosted to 256MB of RAM. Similarly, the iPad contains 256MB of RAM. This discrepancy offers a technical explanation why Apple is not supporting iOS 4 features such as multi-tasking on the original and 3G iPhone -- there simply isn't enough RAM.
iPhone 4 Confirmed to Have 512MB of RAM (Twice the iPad and 3GS) - Mac Rumors http://www.macrumors.com/2010/06/17/iphone-4-confirmed-to-have-512mb-of-ram-twice-the-ipad-and-3gs/
