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 a combination 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, the manufacturer called them '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 suggested the name "Sol" because they were including "the wisdom of Solomon" in the box.

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.