The Altair 8800
Considered by many to be the first microcomputer, the MITS Altair 8800 was based on a 2 MHz Intel 8080 with 256 bytes standard RAM and interfaced with the user through the octal front panel switches.
From InfoCulture: The Smithsonian Book of Information Age Inventions:
It was the Altair 8800, on the January 1975 cover of Popular Electronics, that really set off the (personal computer) boom. A company called MITS, in Albuquerque, sold the Altair for $395 as a kit and $495 assembled.
Within three months 4,000 people had ordered it. Hobbyists who successfully put together their Altairs ended up with a blue, box-shaped machine that measured 17x18x7 inches. To enter programs or data, one set the toggle switches on the front.
There was no keyboard, video terminal or paper tape reader. All programming was in the machine code of binary digits. The first Altair came with only 256 bytes of memory; it also lacked output devices such as printers. Results of a program were indicated by the pattern of flashing lights on the front panel. Through the life span of the Altair, several models were introduced, starting with the original 8800.
The Altair 8800 made its debut in an article that appeared on the cover of the December 1975 issue of Popular Electronics. Within two months the little company MITS, was struggling with thousands of orders. The computer came in kit form and required quite a bit of work and skill to assemble. Users would enter their programs in binary by flipping switches on the front panel of the machine. The output could be read in binary on the LEDs. No software was available for the little machine and users would have to write their own.
The basic unit had only 256 bytes of RAM and cost $395. This configuration made the little machine virtually useless for any real problem solving. However, the system was designed to be expandable with a bus that allowed plug in cards. The bus was to set the standard for the next 5 years (S-100). Within months expansion boards were available to add more memory and attach terminals or teleprinters.
One of the most popular peripherals was Teletype Corporation's ASR-33 teletype. The ASR-33 provided a printer, keyboard, and storage device (paper tape). The company (MITS) would subsequently release newer versions (8800a, 8800b) with more slots and other enhancements, before ultimately losing out in its quest to provide quantity, not quality.