What are good uses of DDR2 and their ilk? As new DDR gens come and go, there never seems to be any discussion on what to do with the old RAM, which is perfectly

What are good uses of DDR2 and their ilk? As new DDR gens come and go, there never seems to be any discussion on what to do with the old RAM, which is perfectly good. Elsewhere in the thread is a mention of gigabyte ramdisk, but what would be really interesting is a second bank you could have on a PCI card that could hold 8 sticks of RAM, and that RAM is considered lower-priority by the OS (use only if the main RAM is getting a bit constrained, or say "use this with the web browser". But I doubt such features exist even in the Linux kernel.