A Brief History of Early PCs
  by Shankar Barua
Photos by Walter Peterson and the
Virtual Computer History Museum

In 1974 Intel introduced the 8080 microprocessor as successor to the 8008. This had a 16 bit address bus and an 8 bit data bus, while internally, there were seven 8 bit registers (six of which could also be combined to make three 16 bit registers), a 16 bit stack pointer and a 16 bit program counter. Intel then updated it's design with the 8085, adding two instructions for interrupts, while reducing power requirement of just +5V.

Most people in the know considered this to be the first microprocessor powerful enough to build a computer around, and with it's clones the 8085 came to dominate the microcomputer industry for the next 4 years.

In December 1975, the Altair 8800 made its public debut in a featured article of of Popular Electronics, and within two months the little company MITS, which made it, was struggling to cope up with thousands of orders.

The computer cost about $395 and came in kit form, requiring quite a bit of work and skill to assemble and operate. Programs were entered in binary code by flipping switches on the front panel of the machine, and output was read in binary from LEDs on the front panel. No software was available for the little machine and users had to write their own.

The basic Altair had only 256 bytes of RAM with no permanent storage, making the little machine virtually useless for any real problem solving. However it was designed to be expandable with a bus that allowed plug in cards, which set the standard for the next 5 years (S-100). Within months of launch, 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, which provided a printer, keyboard, and paper tape storage.

Altair's makers subsequently released newer versions of the machine (8800a, 8800b) with more slots and other enhancements.

One of the first to jump aboard the band wagon after witnessing the instant success of the Altair, was Bill Millard ~ who founded IMS Associates. The computer they designed was very similar to the Altair 8800 with some improvements. Like the Altair, the IMSAI 8080 came in kit form, but Bill's focus was more upon selling the machine to bussiness users. However, without software this proved to be difficult.

The SOL Terminal Computer was built by Processor Technology and designed by the Home Brew Computer Club president Lee Felsinstien. Although originally designed to be a TV terminal, the makers decided to develop it into a full blow computer since it included an 8080 microprocessor. It therefore became the first microcomputer with a built-in video display interface, and was also one of the first to eliminate the need for switchs for entering programs into the computers memory by using ROM memory. The SOL system accepted commands from its keyboard as soon as it was turned on thanks to a monitor program in ROM. It was also sold as a kit.

In 1976, another new personal computer arrived in the marketplace as the Pet 2001, featuring the then new 6502 microprocessor. Commodore International would later buy MOS Technology, the company that produced the 6502. The Pet was one of the first computers to feature a built in display. It's base configuration featured 4K of RAM (expandable to 32K) and a 8K BASIC in ROM. Programs could be stored on cassette, and the selling price was about $595 with 4K and $795 with 8K. Commodore later produced two very low priced computers: the VIC-20 followed by the Commodore 64.

1977 signaled the end of the first phase of the microcomputer revolution with introduction of the Apple II. It came fully assembled and ready to use, mass produced in a molded plastic case. Like the Apple I that came before it, the Apple II was designed by it's maker, Steve Wozniak, to be a powerful yet affordable computer built around the MOS Technology 6502 microprocessor which was available for around $20 in small quantities at the time when Intel's 8080A cost over $150. The system attached to a television with the aid of an RF modulator and could be expanded to hold as much as 48K of RAM. BASIC was pre-loaded in ROM. The Apple II enjoyed many years of success before finally being replaced by an enhanced version, the Apple III.

When first introduced in 1980 as a business machine, the Apple III had been rushed through design and testing into production. Early models were plagued with problems. IC chips even popped out of their sockets while the computer was running! The Apple III was also designed to be Apple II compatible, but emulation of the Apple II was also lacking. Though most of the problems were eventually solved, the damage had already been done and as a result, the Apple III failed to achieve anywhere near the success of it's predeccesor. It used the 6502A microprocessor which ran at about twice the speed of the 6502 used in the Apple II, and allowed expansion to a maximum of 256K of RAM.



PC Beginnings


In the early 1970s, computer professionals and hobbyists still awaited turns to use the few computers available to them in the world at the time.

By the end of 1974 however, the magazine Popular Electronics was regularly receiving plans for personal computers from people around the USA, but Les Soloman, the technical editor who evaluated most of these, didn't believe they were as good as they should be, and eventually contacted a friend to have a go at doing something about it.

Ed Roberts, Les' pal, was the president of an Albuquerque, New Mexico company called MITS. A gadget freak who had received electronics training in the Air Force before launching the company from his garage with a couple of other ex-Air Force officers, Ed had started out by selling mail-order radio transmitters for model airplanes, calling the company Micro Instrumentation Telemetry Systems, which became MITS. By 1969, he'd bought out his partners and moved his company to a larger location, manufacturing calculators and calculator kits for the home hobbyist.

In 1972, Texas Instruments developed their own semiconductor chip and literally wiped out the market for companies like MITS by selling calculators at less than half the going price.

Ed had been toying with the idea of building a kit computer in any case, and when the calculator market fell apart for him in 1974, and his friend Les Soloman got in touch looking for a personal computer to promote, Roberts jumped in feet first. With a price-target set under $500, and Les joining in on some hard core head-banging in development, Ed wanted his computer to be expandable like the new minicomputers that were then beginning to enter big businesses, with individual circuit boards for specific purposes that could communicate internally ~ sort of mimickimg, eventually, a large mainframe in miniature.

When ready, the name for the new machine came from Soloman's 12-year-old daughter, Lauren, who suggested Altair ~ the destination for the Star Ship Enterprise during an episode of Star Trek that she happenned to be watching.

News of the new MITS Altair personal computer was first broken in an article about it in the January 1975 issue of Popular Electronics, which described it as the "World's First Minicomputer Kit to Rival Commercial Models." No one had truly anticipated how primed the market was for an affordable personal computer, and there was an immediate onslaught of orders that Roberts and Soloman could not have imagined in their wildest dreams. Thousands of electronics hobbyists and programmers piled in, with none really still sure of how the computer would be used. Folks just knew of the potential,.. and were desperate to have it.

Roberts' small company couldn't even begin to meet the huge tide of demand for the machine, and as a result, the original Altairs were sent out as big empty boxes with a CPU card containing an Intel 8080 processor, 256 bytes of memory, and a toggle-switch-and-LED front panel. There was no monitor, keyboard or software programs. Entering data required one to manipulate the switches on the front ~one at a time~ for every binary digit. No promised peripherals were delivered with the original order.

The Altair was in fact sold as a kit, with operation dependent almost entirely on the skill of the end-user and builder. Not surprisingly, most of the first machines never even managed to work at all, but that didn't stop the flood of computer-starved hobbyists and programmers clamouring to be among the first consumers. Folks went ahead and bought computers that didn't work, tinkered with them, made them work and wrote programs of all description to work on them. And all the action continued to bring more people in.

Amongst all of this, two programmers in Boston saw the ad for the Altair in Popular Electronics and realized that a program they'd written could work here also. Paul Allen, who had left college to work for TRW and later Honeywell in Boston, and Bill Gates, a freshman at Harvard, immediately got in touch with Ed Roberts.

Initially, Ed was skeptical since dozens of programmers had been approaching him ever since the article appeared, and yet nothing significant had really managed to even run on his machine. But like many of those now-anonymous others, Allen and Gates followed through anyway, and six weeks later demonstrated to Roberts their BASIC program running on an Altair computer, and though it didn't ~at the time~ really do anything much beyond merely announcing its presence, immense possibilities were at last transparent.

Roberts immediately took on Allen as Director (and entire department!) of Software at MITS, while Gates went back to school, only to return again later in1975 to live Albuquerque and work part time writing MITS programs.

When the initial excitement over the appearance of the MITS Altair eventually began abating, it's limitations started becoming evident. The kit contained nothing more than the housing, a power supply, a circuit board with 256 bytes of onboard memory, a front panel board, and a motherboard that was the main piece of circuitry.

There were 18 slots for additional circuit boards, but there were actually no such boards available! To make matters worse, attaching the front panel board required hours of work and dozens of wires before users could even begin to communicate with the computer. Even after setting it up correctly, there was still no permanent storage, which meant that users could put information into the machine and manipulate it, but as soon as they turned the computer off or moved to another application, the information was lost. Temporary storage amounted to only about a paragraph's worth of information at a time, and entering the information using machine language in the form of numeric codes bit by bit through the switches was tedious, time consuming, and awkward.

The BASIC program developed by Allen and Gates did solve the last problem, but itself required 4096 bytes of memory ~ i.e. 16 times the space availabe. Higher density memory boards and a better method for entering programs quickly were desperately needed to move forward. Paul Allen was involved in helping the hardware designers create a 4K (4096 byte) memory board that would allow Altair to run BASIC, but there were problems getting two or more to work together, which was essential to using BASIC and entering data. There was also the problem of how to load and store the BASIC program itself. Allen and Gates had initially used paper tape, but there were serious drawbacks, including expense, expediency, efficiency, and security. Audio-cassette recorders were considered, but proved to be slow and clumsy, but a lead was eventually taken from IBM, which was using disk drives that were expensive but efficient.

Meanwhile, the MITS 4K boards being distributed weren't working! Bill Gates told Roberts that the boards were inadequate, but Roberts insisted that MITS keep sending them out. User frustration mounted in response to this, and an out-of-work hobbyist named Bob Marsh eventually started a company called Processor Technology in April, 1975, which began selling 4K boards that did work. Roberts retaliated by tying purchase of the popular BASIC program to his 4K boards, to prevent erosion of his marketplace, but hobbyists began making their own copies of BASIC and distributing them for free.

Processor Technology continued to distribute its 4K boards and develop other Altair-compatible products, while other companies began developing hardware and software for use on the Altair. To keep up with the competition, he came out with a new computer called the 680b, again attempting to appeal to the masses by creating a low-cost computer. Thousands of orders were again received, but again, there were problems, and even after a complete redesign, the new computer was not very successful.

Meanwhile, more companies came on line, selling boards and chips, software, and even comparable computers. Nevertheless, MITS managed still to hang on to its lead as the primary seller till late 1976, when Commodore bought MOS Technology, a small semiconductor company that had come up with an affordable computer kit built around its own chip.

A large and established company with extensive distribution capabilities had at last entered the microcomputer marketplace, and Tandy Corporation too was looking for an affordable microcomputer to start selling out of its Radio Shack stores. Competition was getting fierce, and MITS was in trouble. It had grown too big too fast and had too many projects going on at the same time. Quality control was hopeless, products were failing, and customers were complaining.

Ed Roberts apparently isolated himself now, accepting no one's counsel, and communication within the company began to break down. By the end of 1976, Paul Allen and Bill Gates both left MITS to devote time to Microsoft, a company of their own that they'd been developing on a back-burner for sometime.

Complicating matters further, Roberts began insisting that retailers selling the Altair should not sell any other brand of microcomputer, which ~unsurprisingly~ went down poorly, and so while MITS was still on top, Commodore and Apple were becoming evermore formidable competitors.

In May 1977, Roberts finally sold MITS to Pertec, a company specialized in disk and tape drives for minicomputers and mainframe computers. He apparently chose Pertec from several other offers because they gave him his own private research and development lab alongwith the freedom to use it exactly as he pleased. Problems however developed when Pertec discovered that MITS came without the rights to BASIC, the program Gates and Allen had written and licensed under their own company, Microsoft, before ever coming to MITS. The issue went to court; Gates and Allen won; Roberts was furious; and Pertec was upset.

The acquisition spelled the end for MITS. Pertec had come in without actually realizing that the company was facing its worst competition to date. New ideas and ways of working were introduced to address the crisis, but the MITS people began quitting in droves. Even Roberts became fed up, left the company, and even left the very industry as well, eventually going to medical school and becoming a doctor. Pertec continued making Altairs for about a year after the acquisition, but within two years, all traces of MITS were gone.

At the end of the day, even though it lasted only a few years, history records MITS with it's Altair as the true root of the personal computer industry. Alongwith the first affordable microcomputer, it also pioneered computer shows, retailing, magazines, users' groups, software exchanges, and many hardware and software products. In an era when the development of microcomputers still seemed impractical if not impossible, MITS built one and forever changed the world for all humankind.