A (hopefully) simple question regarding SLI. 1Gb Card + 1GB Card = 2Gb Card?

[Mysticpuma]

That's the question.

I currently have a 1GB MSI GTX 560 Ti Twin Frozr II/OC which runs virtually everything beautifully. CoD runs okay upto 1680x1050 with a few settings ramped down but I understand that CoD likes video memory.

So I assume that putting another 1GB MSI GTX 560 Ti Twin Frozr II/OC into my system would give me extra speed but would it effectively make the system have 2Gb of video memory (as-well as very fast!).

I'm not quite sure how SLI works other than it splits the drawing of the screen up between the cards (in different ways) but do the cards see wach other and become 2Gb of memory or does each still only see 1Gb of memory but because they are working together they only have half as much processing to do so there is more room for the data to flow?

That's my 'simple' question, cheers, MP