Technology & Medicine › Digital age › Microprocessor (Intel 4004)
Personal computer
1975 (Altair); 1977 (Apple II, PET, TRS-80); IBM PC 1981· Invention or discovery· Communication & computing
Well documentedSolid records, physical evidence or scientific consensus.
A computer cheap and small enough for one person to own and use at home or on a desk.
See it on the Technology & Medicine map →How it works
The Altair 8800, on Popular Electronics' cover in January 1975, was a kit costing about $400, with switches and lights instead of a screen; Bill Gates and Paul Allen founded Microsoft to write software for it. In 1977 the Apple II, Commodore PET and TRS-80 arrived ready-made. The VisiCalc spreadsheet (1979) made PCs business tools. IBM's PC (1981) used outside parts, so other firms built compatible 'clones' that became the standard.
Why it mattered
Computing moved from corporate data centres to individuals and small firms; spreadsheets and word processing reshaped office work, and Microsoft and Apple became giants.
Think of it like
VisiCalc let users change one assumption, like a rent increase, and watch every dependent number update: the pro forma, automated.
How we know
Surviving machines, magazine coverage, company sales records, and US Census surveys: about 8 percent of households had a computer in 1984, and 51 percent by 2000.
Still unknown or debated
Which machine was the first personal computer is debated: the Kenbak-1 (1971), France's Micral N (1973) and Xerox's Alto (1973) all have claims.
Inside this (1)
Connections (4)
▸Electronic computer (Z3, Colossus, ENIAC) shrank into the Personal computerWell documented
The connection
The 1940s computers filled rooms, used thousands of vacuum tubes, and ENIAC cost about $487,000 in 1946 money. Transistors, chips and finally the microprocessor shrank the stored-program design that grew out of that work, a processor running programs held in memory, onto a desk. By 1977 a complete home computer cost about $600 to $1,300.
When and how
ENIAC at the University of Pennsylvania, 1946; the Altair in Albuquerque, New Mexico, 1975; the Apple II in Cupertino, California, 1977.
How we know
The architecture is continuous: PCs use the stored-program design set out in John von Neumann's 1945 report, written from the ENIAC team's work; price and size records trace the shrinking.
Debates and open questions
Whether the PC followed naturally from cheaper chips or also needed California's hobbyist and counterculture movement, as some historians argue, is debated.
▸Microprocessor (Intel 4004) led to the Personal computerWell documented
The connection
The microprocessor made a computer cheap enough for one person. The Altair 8800 used Intel's 8080, a successor to the 4004; the Apple II used the MOS 6502, which sold for about $25; the IBM PC used Intel's 8088. That x86 family still runs most desktop and laptop PCs.
When and how
Albuquerque, New Mexico (Altair, 1975); Cupertino, California (Apple II, 1977); Boca Raton, Florida (IBM PC, 1981).
How we know
Each machine's specifications name its processor; the January 1975 Popular Electronics cover story on the Altair featured the 8080 chip.
Debates and open questions
Intel itself did not foresee home computers; how much the PC owed to chipmakers versus hobbyist groups such as the Homebrew Computer Club is debated.
▸Personal computer was made easy by the Graphical user interface and mouseWell documented
The connection
Early PCs greeted users with a blinking prompt and needed typed commands. The graphical interface replaced commands with pictures: windows, icons, menus and a mouse pointer. Apple's Macintosh (1984) brought it to a mass market, and Microsoft Windows spread it across IBM-compatible PCs, especially Windows 3.0 (1990) and Windows 95.
When and how
Engelbart's lab at SRI in Menlo Park, 1968; Xerox PARC in Palo Alto, 1973; Apple in Cupertino, 1984; Microsoft near Seattle, 1985–1995.
How we know
Product histories and sales show PC use spreading to non-experts as graphical interfaces arrived; Windows 3.0 sold about 10 million copies in two years.
Debates and open questions
How much the interface itself drove PC adoption, versus falling prices and software like spreadsheets that sold well on text screens, is debated.
▸Personal computer brought millions of homes onto The Internet (TCP/IP)Well documented
The connection
Through the 1980s the Internet mainly linked universities and labs. Once homes had PCs, a modem could connect them over the phone line, first to services like CompuServe and AOL, then to the Internet itself. Cheap dial-up access and the first popular web browser, Mosaic (1993), brought tens of millions online by the late 1990s.
When and how
The US and Europe, roughly 1989–2000; The World, in Boston, offered the first commercial dial-up Internet access in 1989, and AOL connected members to the Internet in the mid-1990s.
How we know
US Census surveys show household Internet use rising with PC ownership: 18 percent of homes in 1997, about 42 percent in 2000.
Debates and open questions
PCs were not the main on-ramp everywhere: much of Asia and Africa first went online by mobile phone, skipping the PC entirely.