Ill get in before Destructobot or FAST get here, as they seem to be the local gurus when it come to this kinda stuff
1.PSram is a fast, volatile memory. The Ram expansion for the ds browser uses this to allow for a cache.
Games are usually run from PSram because its a lot faster. The game is deleted as soon as you turn off the power or softreset.
Loading games into PSram is done in second, thats why its preferred to run games from that.
NOR storage is a bit more permanent(not in that sense). The game stays in even after you turn off the ds. This is the type of storage that is similair to what real GBA carts use and that leads to the conclusion that GBA to DS linkage is possible when you load a game to NOR storage.
2.Saving is done by saving your current data to a seperate storage on the card, the third area, 512 kb SRAM (the first and second being PSram and NOR respectively). I believe that saving is done here when saving from PSram, as the limit is 512kb, but NOR can play/save games with 1mbit saves.
If your using the 3in1 expansion tool, everytime you switch games, it will copy what is in your Sram(current Sram save) into the Saver folder, updating your savefile for the game you last played. Then it will delete it and put in the next save.
Because the Sram is battery backed, you wont have to worry about it being lost when you turn off the ds. Also, the battery is charged while playing ds so you wont have to worry about it running out either.
3.see second paragraph of 2
I think this is how it works, im not sure but this is what ive learned from the short time ive been here.
I hope this is clear enough for you.
If this is wrong, please correct me.
P.S.:TROGDOR!!!!!