The MITS Altair 8800 was a build-it-yourself computer based on the Intel 8080 microprocessor, announced as a cover story in the January 1975 issue of Popular Electronics and sold as a kit by Micro Instrumentation and Telemetry Systems of Albuquerque, New Mexico. It is the machine most often identified as the start of the personal-computer era: the first low-cost computer to reach hobbyists in large numbers and to anchor a whole ecosystem of add-on hardware and software.
In its base configuration the Altair was austere. The front panel, described in MITS’s own documentation, consisted of rows of toggle switches and red LEDs. A user entered programs one byte at a time in binary by flipping the address and data switches and depositing values into memory, then watched results in the lights. The base machine shipped with only 256 bytes of memory and no keyboard, screen, or storage. It was, in effect, a working computer reduced to its absolute essentials, which is precisely what made it affordable at the advertised price of under four hundred dollars as a kit.
The Altair’s most consequential design choice was its open expansion bus. Roberts brought the 8080’s signals out to a backplane of edge-connector slots so that memory and interface cards could be plugged in. This bus, with its 100-pin connectors, was soon adopted and cloned by other manufacturers and became the S-100 bus, an early de facto industry standard. Because anyone could build a card that plugged into an Altair, a cottage industry of third-party memory boards, serial and parallel interfaces, and storage controllers grew up around the machine, and compatible “Altair-bus” computers appeared from competitors.
Software followed the hardware. Bill Gates and Paul Allen wrote a BASIC interpreter for the Altair, demonstrated it to MITS, and licensed it as Altair BASIC; the company they formed to do so became Microsoft. Altair BASIC let users write programs in a high-level language once they had added enough memory and a terminal, transforming the machine from a switch-and-light curiosity into a usable computer. The Altair also became a touchstone at the Homebrew Computer Club, where members built, extended, and argued about it.
Commercially, MITS struggled to keep up with demand and with the competitors its own open bus had enabled, and the company was sold to Pertec in 1977. But the Altair’s historical importance is settled: it proved there was a real market for an affordable personal computer, established the 8080-and-open-bus pattern that the early industry followed, and gave the first generation of personal-computer enthusiasts, entrepreneurs, and software companies their starting point.