The accidental design of the IBM PC character set that defined early computing

Countries & Cities · Published 3 October 2026 Swipe more like this →

In short: Before modern fonts, the IBM PC relied on Code Page 437 to display text. This 8-bit character set introduced the iconic smiley faces, box-drawing symbols, and Greek letters that defined the DOS era. While its origins remain debated, its legacy persists in Windows Alt codes and modern terminal displays.

Code Page 437, or CP437, served as the foundational character set for the original IBM PC. It provided 256 unique 8-bit codes, assigning a graphical character to every position, including those traditionally reserved for non-printing control characters. This design allowed early machines to render text, icons, and complex line-drawing symbols directly from ROM, a feature that remains embedded in the core of VGA-compatible graphics cards today.

The origin story of these characters is surprisingly murky. Bill Gates once claimed the set was inspired by Wang word-processing machines, specifically citing the inclusion of smiley faces and boxes. However, this account is contested, as the Wang character set did not actually contain those specific symbols. Another perspective comes from David J. Bradley, who recalled the character set being finalized during a four-hour plane trip between Seattle and Atlanta, involving himself, Andy Saenz, and Lew Eggebrecht.

The set was structured with internal logic: rows 0 and 1 contained decorative dingbats, rows 2 through 7 held standard ASCII, and rows 11 through 13 provided the block-drawing characters essential for early user interfaces. Hardware circuitry in the IBM Monochrome Display Adapter even duplicated the eighth pixel column of these block characters to ensure lines appeared seamless on screen. While CP437 was limited in its support for Western European languages—lacking specific characters for French, Portuguese, and Icelandic—it established a standard that later sets like CP850 and CP852 sought to improve while maintaining compatibility.

Today, the legacy of CP437 survives through Windows Alt codes, where users can still input characters by holding the Alt key and typing specific numbers. Although modern systems have moved toward Unicode, the original graphic characters are still widely supported in fonts and terminal emulators, ensuring that the visual language of the early IBM PC remains accessible on contemporary machines.

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