Inventors Of The Modern Computer The First Hobby & Home Computers Scelbi - Mark-8 - Altair - IBM 5100

In the early 1970s, anyone wanting to use a computer had to wait in a long line as computers were few and far apart. The desire and the market was increasing for a computer that could be used at home or in the office, the "personal computer". Several different manufacturers marketed "personal computers" between 1974 and 1977 in response to that desire. These were mainly kits (major assembly required) advertised in the back pages of magazines like Popular Science.

In the March, 1974, issue of QST magazine there appeared the first advertisement for a "personal computer." It was called the Scelbi (SCientific, ELectronic and BIological) and designed by the Scelbi Computer Consulting Company of Milford, Connecticut. Based on Intel's 8008 microprocessor, Scelbi sold for $565 and came with 1K of programmable memory, with an additional 15K of memory available for $2760. The second "personal computer kit" was the Mark-8 (also Intel 8008 based) designed by Jonathan Titus. The July issue of Radio Electronics magazine published an article on building a Mark-8 microcomputer, information the general public was hungry for. At the same time, the Intel company introduced the new 8080 microprocessor chip, made for controlling traffic lights. It was to become the microprocessor inside the very successful Altair computer.
 

An Albuquerque, New Mexico, company called MITS (Micro Instrumentation Telemetry Systems) was in the calculator business until Texas Instruments swept the market in 1972 with their low cost calculators. MITS owner Ed Roberts, a former air force electronics specialist, then decided to try designing a computer kit. He was aided by his friend Les Soloman, who happened to be the technical editor for Popular Mechanics magazine and had been flooded with letters from readers describing ideas for home computers. Roberts worked together with hardware engineers William Yates and Jim Bybee during '73 and '74 developing the MITS Altair 8800. The Altair was named by Soloman's 12 year-old daughter after an episode from the original Star Trek television series.

The Altair was the cover story for the January, 1975, issue of Popular Electronics, which described the Altair as the "World's First Minicomputer Kit to Rival Commercial Models". The orders for the Altair were huge in response to the article. The computer kit was shipped with an 8080 CPU, a 256 Byte RAM card, and the new Altair Bus design (S100 Bus - the connector had 100 pins) for the price of $400. It was left to the consumer to put it together, make it work and write any needed software. This was an uneasy task but the computer was definitely expandable, cheap and available.

Two young programmers realized that a software program already written for microcomputers could work on the Altair. Ed Roberts was soon contacted by Harvard freshman Bill Gates (of Microsoft fame) and programmer Paul Allen. Within six weeks, Gates and Allen compiled a version of BASIC to run on the Altair. Allan was offered a position by Roberts as the Director of Software and the only member of the software department. Gates, who was then still a student, started working for MITS part-time after he left school.

BASIC required 4096 bytes of memory to run, sixteen times the amount of memory the Altair then came with. MITS created a 4K (4096 byte) memory board that allowed the Altair to run BASIC. The boards were poorly designed and created problems, and a computer hobbyist named Bob Marsh designed a better 4k board and started a company called Processor Technology to sell his Altair compatible boards. Roberts tried to prevent losing his sales by the BASIC software only with his boards. He succeeded in promoting the first wide-spread case of software piracy. Hobbyists everywhere bought a Processor Technology memory board and somehow found a free copy of BASIC.

Robert's tendency to ship some poorly designed products might have caused MITS' downfall after a few short years, but no one can deny that it was the Altair which really kick-started the home computer revolution. Gates and Allen went on to start Microsoft, becoming the world's leading software developers.

One more computer worthy of note during this period was the IBM 5100. The 5100 was released in 1975 after two years of development. It was referred to as "Project Mercury" by the IBM scientists. The 5100 was IBM's first portable computer and considered an entry level system, but its $10,000 price tag put it beyond the range of the hobbyists who bought the Altair. Sales of the 5100 went to small business and educational institutions who bought the desktop sized minicomputer which came with BASIC, 16KB of RAM, tape storage and a built-in 5-inch screen.

In our next feature: Apple I, II, Radio Shack's TRS-80 and Commodore PET, more of the first hobby and home computers.
 

Related Links

The Story Behind The Altair
An expanded version of the Altair's history with humorous details, including Microsoft's first lawsuit.
Ed Roberts Interview With Home Brew Magazine
Ed fills us in with details like who was the most famous person to buy an Altair.
History Of The Microcomputer Revolution
Read the transcripts originally from a PBS radio show called Computer Bytes News.
Altair 8800
View original Altair 8800 schematics, sales invoice and pictures.
The SCELBI-8H MiniComputer
A proud owner of an original Scelbi states, "In the spring of 1974, ads began showing up for the Scelbi minicomputer kit, the first hobby computer based on the Intel 8008 microprocessor chip. I mailed away for the free brochure, and here is what I received." Read a copy of the original brochure.