I recently found a very cool short paper (4 pages) which
Dennis Gabor written 40 years ago.
It explains the math of associative holographic memory, which turns out to be very simple.
Because it is that simple, neither holograms, nor even waves and oscillations, are actually necessary to implement this scheme of associative memory.
D. Gabor, Associative Holographic Memories, IBM Journal of Research and Development, 13(2), 156-159 (1969).
Abstract,
PDF