  We report our findings of an 1/f power spectrum for the total amount of sand
in directed and undirected Bak-Tang-Wiesenfeld models confined on narrow
stripes and driven locally. The underlying mechanism for the 1/f noise in these
systems is an exponentially long configuration memory giving rise to a very
broad distribution of time scales. Both models are solved analytically with the
help of an operator algebra to explicitly show the appearance of the long
configuration memory.
