Sixty-four — squares of the chessboard

The chessboard is 8×8 = 64 squares. Chess was invented in India around the 6th century AD. The number 64 = 2⁶ makes the chessboard an ideal space for binary logic and computer algorithms.

Modern processors are 64-bit: they process 64 bits of information simultaneously and can address up to 16 exabytes of memory. The transition from 32 to 64 bits in the 2000s was a key leap in computing power.

The I Ching (Book of Changes) — one of the oldest Chinese texts — contains exactly 64 hexagrams. Each of the 64 possible combinations of six lines symbolizes a certain state of the universe.