Introduced in June 1976 at the PC'76 computer conference, the SOL-20 was designed by Lee Felsenstein, who also was one of the founders of the Community Memory Project, moderated the meetings of the Homebrew Computer Club from 1975 until 1986, and designed the Osborne 1. Like the Atair and IMSAI machines, the SOL-20 is an S-100 bus machine with 5 S-100 slots and used the 8080 as it's CPU. Unlike the other S-100 machines of the period, the S-100 slots are mounted so that the cards lay horizontally, one above the other. Also unlike the Altair and IMSAI machines, the SOL-20 included the video and I/O functions needed to use the machine, including a tape interface, on it's mainboard, as well as provided various ROMs, called 'personality modules'. Among the items Processor Technology sold for the SOL were additional SRAM and DRAM memory boards and a high-capacity HELIOS disk subsystem. The HELIOS disk system proved unreliable in use though so other disk systems from manufacturers such as North Star were popular. While some have called 1975 the year of the Altair and 1976 as the year of the IMSAI, 1977 has been called the year of the SOL. It was one of the first systems marketed as a complete, usable system vice a barebones system that needed to be expanded in order to even be used. The built in I/O and video systems in the SOL were based on S-100 bus expansion cards that Processor Technology had previously released as upgrades for other machines. The SOL-20 was housed in an attractive blue colored steel case with solid walnut side panels. The keyboard was manufactured by Keytronic and carries a manufacture date of 3/78. Amazingly, there are some parts on the keyboard that interchange with their keyboards manufactured nearly 25 years later.
Initially, there were to be three variants on the SOL produced:
It's unclear if either the SOL-10 or SOL-PC were sold in any number. According to Mr. Felsenstein, it is estimated that approximately 12,000 SOL-20's were produced. Initially, both the cassette recorder for program storage and modified TV for the display were produced by Panasonic. The SOL shipped with a small BASIC interpreter on tape, though a more capable 8k BASIC was available. There was also a newsleter, called 'SOLUS', published.
This particular machine retains it's original Panasonic TV monitor and cassette recorder. It was orignally purchased in Santa Clara, California in early 1978 and was used to write programs to control KENO machines. It has three memory boards installed, two 16k DRAM boards manufactured in April 1978 and the 8k SRAM board that was bought with the machine. At the time, each of the 16k DRAM boards listed for over $500 each.