The Processor Technology Sol-20 Terminal Computer (S/N 102538) came with the following four S-100 boards: 
The plug-in "personality module" is an early type based on four 512-byte National Semiconductor 5204 ROMs, each labeled "4.1" and individually as S0, S1, S2, and S3. "S2" is a gray ceramic, while the other three are purple. The CPU is a white ceramic AMD C8080 with date code 7550 and the motherboard is Rev. D, S/N 303848 (hand written in white-out). Most of the ICs are date-coded to mid-1976, with some of the more common TTL chips dating to 1975. The serial number and model tag indicates that the machine was originally sold as a Sol-10. Possibly it was upgraded to the Sol-20 model with the addition of the expansion riser and replacement or refurbishment of the power supply and keyboard. The riser 100 pin expansion slots are dated mid-1977, so appear to be of later vintage than the other components. The Sol-20 was designed by Bob Marsh, Lee Felsenstein and Gordon French in mid-1976. It was featured as a project in the July 1976 issue of Popular Electronics and later that summer at the first Atlantic City Computer Show in August. The first units were delivered in December 1976, a year after shipments of the IMSAI 8080 began. The Sol is quite remarkable compared to the other machines of the early microcomputer era, especially the Altair 8800 and IMSAI 8080. With the inclusion of on-board video, relatively simple connectivity to a monitor (or modified TV), and a keyboard (with 84 keys, no less), the Sol represented a rapid expansion of features that would become standard in the next generation of "appliance computers," like the Commodore PET, Apple II, and Radio Shack TRS-80. The resemblances between the Apple II (released in late 1977) and the Sol are striking, not only because both included video output and a keyboard. They had several other similar attributes: their physical wedge-like design, single motherboard architecture (in lieu of the backplane design popularized by the Altair 8080), regulated power supply, expansion slots, and on-board tape recorder support for storage. The Sol also included the capability to control the tape drive motor and, even more impressively, had built-in parallel and serial ports. Communication ports wouldn't become integrated into Apple computers until the Apple //c and Macintosh were introduced in 1984. The later Apple II clearly benefited from the use of a switching power supply, which reduced the weight of the machine considerably, and its uncomplicated design—a simple metal plate and the classic plastic shell—which likely meant it was cheaper to manufacture than the complex sheet metal (and walnut!) of the Sol. I imagine that the common features of the Sol-20 and Apple II reflects the activity and ideas flowing among the microcomputer community at the time, notably at meetings like the Homebrew Computer Club. After all, the Apple I was a single-board microcomputer with video output and a cassette interface, too. The other interesting characteristic of the Sol was that it had still retained features of the other S-100 systems, including DIP switches on the PC board that functioned as the front panel "sense switches" on the Altair and IMSAI, S-100 expansion slots, and access to unregulated 8 and +/- 16V power. Microcomputers were evolving rapidly and converging on a common form factor of the appliance device. The Sol is an interesting machine that reflects this transition. The Sol-20 I bought was in reasonably good physical condition and unknown operating condition. This Sol-20 wasn't a "plug it in and go" restoration by any means. First, the fuse holder cap had been sheared off and the entire fuse assembly required replacement before any real work could begin. There were a number of missing machine screws throughout the computer. Clearly, it had been worked on extensively at some time, but its dusty state suggested that it had been many years ago. Since all of the IC date codes were 1976 vintage, none of them appeared to have been changed, but a few had traces of soldered pins, either from jumpers or as repairs. The wood sides were in good condition, but the finish had faded. Were the 40 year old ROMs good? Had the processor survived? The bus drivers and logic? RAM? The first order of business would be getting the power supply up and running and tested out. |