The Altair 8800 from MITS (Micro Instrumentation and Telemetry Systems) was the first mass-produced personal computer to be openly available. It was introduced in January, 1975, as a kit; later, pre-assembled units were made available.
It was a microcomputer, built around an Intel 8080 microprocessor. The early 8800's were unreliable, and had a weak power supply; the later 8800a was better, but it was only with the 8800b that it became really reliable. It originally came with no peripherals, just a front panel; later, a variety of optional add-on units, including a floppy disk drive, were made available.