How does SLI memory work?

[Ipno]

Begging forgiveness if this has been discussed before, I searched and couldn't find anything.

If I put two 256 meg cards in SLI mode on a system, is that the same as having one card with 512 megs of memory, or do they have to load the same stuff twice, leaving you with essentially 256 megs of memory anyway?

 

[Matthias99]

The latter. They don't share memory.

And yes, this HAS been discussed before, and was discussed in just about every SLI launch article.