Another quandary, chaps. 

To get the power low in Balloon, it's time to start supporting low-
voltage, mobile-oriented SDRAM. All well and good. However, it's 
also available in BGA, which would let me save some space - also 
good. (In fact, quite a lot of space - a TSOP54 package, like we 
use on Balloon2.0x takes 312mm^2, and an 8x11mm FBGA takes  
130mm^2. However, you can't stack BGA packages like you can 
SOP, for the real density obsessives. Current RAM seems to offer 
up to 256Mbit / package in mobile form, 512Mbit in 'regular' 
SDRAM. 
Balloon2.0x allowed us to fill all 4 banks of the SA1110 
(128MBytes each) for a total of 512MBytes (in theory - I don't 
think anyone ever built one that massive, did they?). 
If Balloon3.x only supports BGA packages, it'll be limited to a 
depressingly low 64Mbytes with current parts. It seems to me that 
this isn't enough headroom. I could fit 2 pairs of BGA devices, but 
that seems futile.  - unless we expect the future to bring us 
mobile SDRAM, in BGA, in 512Mbit or above. Anyone got a 
working crystal ball I can borrow for a while?

Upshot - I currently favour TSOP 54 packaging, now that mobile 
die are available in that package. It's not the best of all worlds, 
but I think the flexibility is handy. Would anyone suggest a 
different tack? (Socketed memory / SODimms are right out, before 
anyone suggests it). 
Note that this doesn't affect the NAND / Boot flash in any way - 
just because PPC people call everything 'memory' doesn't mean 
that we have to...


Steve