16-bit
The middle chapter of computing history: enough for real programs, but only 65,536 addresses to put them in.
Word size states how many bits the processor works with at a time. Sixteen bits give integers up to 65,535 and — the part that actually caused trouble — a directly addressable space of 64 kibibytes. Intel's 8086 worked around this with segmentation, where an address was assembled from two registers, a solution that shaped PC programming well into the 1990s.
The era ran roughly from the mid-1970s to the early 1990s and covers the 8086, the Motorola 68000 and the games consoles marketed on precisely that number. The term survives in two contexts: as a description of a graphical style with a limited palette and visible pixels, and in compounds like 16-bit floating point, the format that made neural networks cheap to train.