Nice techy piece on the theory and practice of atomic-scale memory.
A two-dimensional version of Feynman's atomic memory is formed on the surface of silicon by a small amount of gold (below on the right). It looks similar to the CD-ROM on the left, but the scale is in nanometers instead of micrometers. That means the storage density is a million times higher. Extra silicon atoms (white) sit on top of self-assembled tracks that are formed by the gold. Each track is exactly five atoms wide. It is suggestive to assign an extra silicon atom to a 1 and a vacancy to a 0. The minimum empty area required around each bit is 5×4=20 atoms, 4 atoms along the track and 5 atoms from one track to the next. Feynman's 1959 suggestion of spacing the bits 5 atoms apart was right on the mark.
(Thanks, Bruce!)
