Can someone explain the example with the ramdisk? It's not clear to me how a ramdisk is relevant to the problems put forward in the paper, i.e. disk is too slow

Can someone explain the example with the ramdisk? It's not clear to me how a ramdisk is relevant to the problems put forward in the paper, i.e. disk is too slow, they rely on lazy page allocation, and they have insufficient ram to hold two copies of everything simultaneously.