Two Stop Bits

The 80×24 and 80×25 terminal display sizes are not the result of inevitable technical constraints but rather IBM's market dominance. The 80-column standard traces back to IBM's 80-column punch cards (1928). The 24-line standard was set by the IBM 3270 terminal (1971), which used four banks of 480-character shift registers and captured 50% of the terminal market, forcing competitors to match its dimensions. The DEC VT100 (1978) followed this 80×24 standard. The 80×25 variant came from the IBM PC (1981), which inherited much of its design from the obscure IBM DataMaster and squeezed an extra line onto the display. Early 1970s terminals showed wildly diverse sizes (31×11 to 133×64), proving technology didn't dictate a single size — market standardization around IBM products did. The IBM 2260 (1965), the first major CRT terminal, used exotic sonic delay lines (50-foot nickel wires storing bits as sound pulses) for pixel storage, and its 80×12 display made 80×24 the natural next step for IBM.

IBM, sonic delay lines, and the history of the 80×24 display

Some theories about the 80×24 and 80×25 sizes