Three machines reaching buyers in 1977, from Apple, Commodore and Tandy, created a consumer market for computers sold as finished products rather than kits. Games spread through user groups, magazines that printed listings for readers to type in by hand, and cassette tapes traded between friends. IBM's entry in 1981 brought corporate credibility and, because it was assembled largely from parts anyone could buy, invited compatible clones. That accident of openness eventually made the compatible PC the most widely supported gaming platform in existence.
The open architecture set the rhythm. Owners upgrade rather than replace, so the platform improves continuously instead of in generations, and developers target a range of machines instead of one fixed specification. Sound cards, then 3D accelerator cards in the mid-1990s, then a steady cadence of graphics hardware created an upgrade cycle with no equivalent on consoles. It also produced things closed platforms discouraged: shareware, level editors, modifications made by players, and eventually storefronts that let a developer sell directly.
Regional history matters here more than anywhere else in the archive. Britain's inexpensive keyboard computers created a bedroom coding culture in the 1980s, 16-bit machines from Commodore and Atari led European gaming into the 1990s, and separate ecosystems grew up in Japan and elsewhere. Entries filed under this platform range from hardware and operating environments to whole genres that existed because a keyboard and a large screen were available: strategy games, simulations, interactive fiction and the first-person shooter. Digital storefronts and player-made modifications belong here too, since both arrived first on machines nobody had to ask permission to publish for.