The RAM is not part of the SoC and is not supplied by TI.Yes, you can mount it on top (to save space/cost) but you don't need to, there are designs using same OMAP with separate RAM chips. The parts (OMAP chip, RAM/NAND chip) are bought separately and are soldered in factory just like other components. For available parts see http://www.micron.com/products/mcps/

The biggest RAM Micron lists even today is 2gb=256MB. When N900 was designed there was possibly no other option. Today there is 512MB available too, see http://igep-platform.com/shop/index....products_id=23 but that option was not available few months ago.

As for the Qualcomm SoC, not sure about Snapdragon but previous chips (MSM7200A) say it has 288 RAM but only ~180MB is really available to Windows Mobile. And when device boots most of it is already used. My Touch Diamond2 has 183MB of program memory (RAM) and 111MB is already in use when no user application is running.

I guess they are cheating somehow and count also RAM reserved for radio module or something. I wonder how much of that HD2's 448MB RAM is really available as program memory and how much is free when system boots.