Sol-20
The Sol-20 was the first fully assembled microcomputer with a built-in keyboard and television output, what would later be known as a home computer. The design was the integration of an Intel 8080-based motherboard, a VDM-1 graphics card, the 3P+S I/O card to drive a keyboard, and circuitry to connect to a cassette deck for program storage. Additional expansion was available via five S-100 bus slots inside the machine. It also included swappable ROMs that the manufacturer called 'personality modules', containing a rudimentary operating system.
The design was originally suggested by Les Solomon, the editor of Popular Electronics. He asked Bob Marsh of Processor Technology if he could design a smart terminal for use with the Altair 8800. Lee Felsenstein, who shared a garage working space with Marsh, had previously designed such a terminal but never built it. Reconsidering the design using modern electronics, they agreed the best solution was to build a complete computer with a terminal program in ROM. Felsenstein mentioned on a recent interview that the name of the Sol was inspired after Les Solomon, Technical Editor of Popular Electronics.
The Sol appeared on the cover of the July 1976 issue of Popular Electronics as a "high-quality intelligent terminal". It was initially offered in three versions; the Sol-PC motherboard in kit form, the Sol-10 without expansion slots, and the Sol-20 with five slots.
A Sol-20 was taken to the Personal Computing Show in Atlantic City in August 1976 where it was a hit, building an order backlog that took a year to fill. Systems began shipping late that year and were dominated by the expandable Sol-20, which sold for $1,495 in its most basic fully-assembled form. The company also offered schematics for the system for free for those interested in building their own.
The Sol-20 remained in production until 1979, by which point about 12,000 machines had been sold. By that time, the "1977 trinity" —the Apple II, Commodore PET and TRS-80— had begun to take over the market, and a series of failed new product introductions drove Processor Technology into bankruptcy. Felsenstein later developed the successful Osborne 1 computer, using much the same underlying design in a portable format.
History
Tom Swift Terminal
was one of the sysops of Community Memory, the first public bulletin board system. Community Memory opened in 1973, running on a SDS 940 mainframe that was accessed through a Teletype Model 33, essentially a computer printer and keyboard, in Leopold's Records record store in Berkeley, California. The cost of running the system was untenable; the teletype normally cost , the modem another, and time on the SDS was expensive - in 1968, Tymshare charged per hour. Even the reams of paper output from the terminal were too expensive to be practical and the system jammed all the time. The replacement of the Model 33 with a Hazeltine glass terminal helped, but it required constant repairs.Since 1973, Felsenstein had been looking for ways to lower the cost. One of his earliest designs in the computer field was the Pennywhistle modem, a 300 bits per second acoustic coupler that was the cost of commercial models. When he saw Don Lancaster's TV Typewriter on the cover of the September 1973 Radio Electronics, he began adapting its circuitry as the basis for a design he called the Tom Swift Terminal, a reference to the fictional scientist and inventor of the same name. The terminal was deliberately designed to allow it to be easily repaired. Combined with the Pennywhistle, users would have a cost-effective way to access Community Memory. Marsh and Felsenstein reconnected once Marsh finished building his TV Typewriter in 1974. When Felsenstein saw it, he began to design his own terminal, which he hoped to deploy as a replacement for Community Memory teletypes.
In January 1975, Felsenstein saw a post on Community Memory by Bob Marsh asking if anyone would like to share a garage. Marsh was designing a fancy wood-cased digital clock and needed space to work on it. Felsenstein had previously met Marsh at school and agreed to split the rent on a garage in Berkeley. Shortly after, Community Memory shut down for the last time, having burned out the relationship with its primary funding source, Project One, as well the energy of its founding members.
Processor Technology
January 1975 was also the month that the Altair 8800 appeared on the front page of Popular Electronics, sparking off intense interest among the engineers of the rapidly growing Silicon Valley. Shortly thereafter, on 5 March 1975, Gordon French and Fred Moore held the first meeting of what would become the Homebrew Computer Club. Felsenstein took Marsh to one of the meetings, Marsh saw an opportunity supplying add-on cards for the Altair, and in April, he formed Processor Technology with his friend Gary Ingram. The company proposed their own 8080 board to effectively create the new computer. But, Felsenstein declined the offer to design it, and the project was scrapped.The new company's first product was a DRAM memory card for the Altair. A similar card was already available from the Altair's designers, MITS, but it was almost impossible to get working properly. Marsh began offering Felsenstein contracts to draw schematics or write manuals for the products they planned to introduce. Felsenstein was still working on the terminal as well, and in July, Marsh offered to pay him to develop the video portion. This was essentially a version of the terminal where the data would be supplied by the main memory of the Altair rather than a serial port.
The result was the VDM-1, the first graphics card. The VDM-1 could display 16 lines of 64 characters per line, and included the complete ASCII character set with upper- and lower-case characters and a number of graphics characters like arrows and basic math symbols. The VDM-1 freed thousands of hobbyists from tediously entering programs via toggle switches, the noise, expense, and maintenance requirements of a teletype, and the cost and extra space required for a proper terminal. An Altair equipped with a VDM-1 for output and Processor Technology's 3P+S card running a keyboard for input removed the need for a terminal, yet cost less than dedicated smart terminals like the Hazeltine.
Intelligent terminal concept
Before the VDM-1 was launched in the fall of 1975, the only way to program the Altair was through its front-panel switches and LED lamps, or by purchasing a serial card and using a terminal of some sort. This was typically a Teletype Model 33, which still cost $1,500 if available. Normally the teletypes were not available Teletype Corporation typically sold them only to large commercial customers, which led to a thriving market for broken-down machines that could be repaired and sold into the microcomputer market. Ed Roberts, who had developed the Altair, eventually arranged a deal with Teletype to supply refurbished Model 33s to MITS customers who had bought an Altair.Les Solomon, whose Popular Electronics magazine launched the Altair, felt a low-cost smart terminal would be highly desirable in the rapidly expanding microcomputer market. In December 1975, Solomon traveled to Phoenix to meet with Don Lancaster to ask about using his TV Typewriter as a video display in a terminal. Lancaster seemed interested, so Solomon took him to Albuquerque to meet Roberts. The two immediately began arguing when Lancaster criticized the design of the Altair and suggested changes to better support expansion cards, demands that Roberts flatly refused. Any hopes of a partnership disappeared.
Solomon then traveled to California and approached Marsh with the same idea, stating that if they could produce the design within 30 days, he would put it on the cover of the magazine. Marsh once again hired Felsenstein to design the system. As Felsenstein later noted:
Design effort
Felsenstein initially wanted to build a terminal following the model of his earlier Tom Swift design, using discrete electronics. Marsh, in parallel, sketched out a version using the Intel 8080 in April 1976, in which the terminal was titled the "Sol-1" at the time. The new machine was meant to maintain compatibility with the Altair 8800 and the S-100 bus. It quickly became apparent the difference in cost would only be about $10, and from then on the original dedicated terminal concept was dropped. Over time the plans changed, and at some point, Marsh told Felsenstein "We want you to design a computer around the VDM display."Initially, the idea was to sell a kit system, as was common in the industry at that time. The kit concept would make it through to the release, at which time it was known as the Sol-PC. As the design process continued, at some point the decision was made to offer the system in complete form, with all the parts needed for a complete system.
Felsenstein originally thought he was only needed for the initial design, but as the physical layout began it was clear that the layout artist they had hired would not be able to do it on his own. Marsh had a woodworker friend build a large light table and Felsenstein and the layout artist began using it to design the printed circuit board for the motherboard. While Felsenstein worked on the design, Marsh continually came up with new ideas that he demanded to be included. This led to creeping featuritis problems and the final design was not delivered until about two months of "frantic" work.
The final product consisted of a single motherboard with the 8080, a simplified version of the VDM-1, serial input/output, and 1k of SRAM for the screen buffer. A ROM, the "personality module", would include the terminal driver or other code which would begin running as soon as the machine was turned on. The module was designed so it could be removed or inserted without accessing the interior of the machine.
Marsh, meanwhile, was working on the physical design. He demanded from the start that it use walnut sides; while working on the digital clock project he had learned from his woodworker friend that they could get parts for practically nothing if they were small enough to be made from off-cuts. Beyond that requirement, anything was fair. The deadline for the magazine had been pushed back, but there was still little time to finalize the layout before it needed to be photographed. Marsh decided that the machine should have a cassette deck, so they mocked up a machine with a keyboard on the left and cassette player on the right.
The first motherboard arrived 45 days after the project started, and the first cases and power supplies about 15 days after that. By this point it was clear the system was a usable microcomputer on its own, but "the decision was made to soft-pedal the fact until the last possible moment. Once published, all the fuss possible was to be made about its general-purpose nature; but until it actually saw print, it was to be treated first as a terminal."
As the machine increasingly expanded in power, Felsenstein suggested the name "Sol", because they were including "the wisdom of Solomon" in the system. Les Solomon would later quip that "if it worked, they'll say Sol means 'sun' in Spanish. If it don't work, they're gonna blame it on the Jewish guys." Stan Veit later joked to Solomon that they named it after him in another way, "the LES Intelligent Terminal".