IBM, sonic delay lines, and the history of the 80×24 display
This fascinating historical deep-dive unravels the true origins of the ubiquitous 80x24 and 80x25 terminal display sizes, debunking common technical explanations. It argues that market dominance, primarily by IBM's successive generations of terminals and eventually the PC, dictated these standards rather than inherent technological limitations. Hacker News readers appreciate this meticulous historical research that challenges widely held assumptions about computing history.
The Lowdown
The article investigates the persistent mystery behind the widespread adoption of 80x24 and 80x25 character terminal display sizes, often attributed to technological constraints like TV aspect ratios or memory limits. Author Ken Shirriff meticulously debunks these popular theories, instead tracing the lineage of these standards primarily to the market dominance of IBM's terminal products over several decades.
- Common theories for 80x24/80x25, such as VT100 compatibility, 2K RAM limits, or TV aspect ratios, are shown to be flawed or incomplete upon closer historical and technical inspection.
- Early CRT terminals exhibited a vast array of screen sizes (e.g., 31x11, 133x64), demonstrating that technology alone did not inherently dictate a specific standard.
- The 80-column width originated from punch cards, a well-established standard before CRT terminals.
- IBM's first major entry, the 2260 Display Station (1965), though offering 40x12 or 80x12 displays, internally processed 80x24, popularizing the CRT concept. It famously utilized sonic delay lines for memory, a technology sensitive to temperature and vibration but cheaper than core memory.
- The IBM 3270 (1971) truly cemented the 80x24 standard, leveraging more advanced MOS shift registers and becoming the market leader, compelling competitors to adopt compatible sizes.
- The subsequent shift to 80x25 was driven by the IBM PC (1981), which adopted its display parameters from the earlier, obscure IBM DataMaster. The PC's designers were able to squeeze in an extra line, differentiating it and establishing the 80x25 as a new PC-centric standard, without a strong technical or compatibility imperative.
Ultimately, the article posits that the evolution of 80x24 and later 80x25 display standards was less about an inevitable technological convergence and more a testament to IBM's pervasive influence and market-setting power, from mainframe terminals to personal computers. This legacy continues to shape modern terminal windows, reflecting a historical compromise between design and market forces.