One's brain, or, more specifically, one's collection of memories (and capacity for additional memories). An allusion to the notion that one's mind is like a sponge.
cf. hard drive, floppy drive, thumb drive
cf. hard drive, floppy drive, thumb drive
"I can’t remember much more... Hard drives nearing full. Sponge drive doesn’t work so well for digital assets."
by subpixel April 25, 2009