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The SOL-20 Terminal Computer

Manufacturer Processor Technology
Model Sol-20 Terminal Computer
Date Announced 1976
Date Canceled Unknown
Number Produced About tens thousand
Country of Origin USA
Price $1,000 kit, $2,000 assembled
Current Value $250 and up
Processor Intel 8080
Speed 2 MHz
RAM Usually 8K-64K
ROM 1 or 2K ROM, 1K video
Storage Cassette tape, 5.25" and 8" disk
Expansion 5 expansion slots
Bus S-100
Video 64x16 black and white text
I/O Parallel, Serial
OS Options CP/M, BASIC, NorthStar DOS and a variety of others
Notes The SOL-20 was probably the first PC to incorprate a keyboard and video with the machine. This form factor obviously became the norm when the Apple ][ debuted a year or more later. The SOL also included ROM "personality modules" that allowed the computer to have some native code at power on. Other than that, however, the SOL-20 was a fairly typical S-100 system in a different package.
Related Items in Collection MITS Altair 8800, IMSAI 8080 and a variety of other S-100 systems.
Related Items Wanted Helios disk subsystem, additional personality modules, additional software, expansion chassis, etc.

Processor Technology was started as an add-in card company producing mainly memory cards for the MITS Altair 8800. Like many similar companies, they quickly expanded into producing competing systems themselves.

The SOL-20, designed by Lee Felsenstein and conceptualized by Bob Marsh and Les Solomon, was a seminal personal computer that was first to include integrated keyboard, video and ROM in the same package. This model quickly became the industry standard for user friendly personal computers.

The Sol-20 was an 8080 based system that incorporated the Processor Technology VDM-1 to produce video on a television or composite monitor. The system included a monitor ROM that allowed the user to boot the machine into a semi-usable mode on power up.

The machine in my collection is in exceptionally good condition and works perfectly.

The guts of the SOL-20 from the front

The SOL-20 had a very clean design with a large motherboard, a five slot S-100 card cage and a relatively small power supply.

The SOL-20 interior from the back

From the back you can get a clear shot of the card cage and the "personality module" on the bottom right.

A screen capture from the SOL-20

The SOL-20 runs perfectly and a quick memory dump can be seen here on a standard composite monitor hooked up to the system.

I've got a manual around here somewhere. As soon as I dig it up I'll post pictures.

(Submitted December 12, 2011 18:49:35 by Chief)

I read the recent Steve Jobs book. The Sol 20 is metioned in there as the benchmark for the integration of Apple 1 components into the Apple 2. Jobs claimed it was the best looking unit of the show.

(Submitted April 30, 2011 14:47:21 by Roland Dufault)

Hi, being a Ham Radio operator that loveed Morse code, I purchased the Sol 20 Computer in 1976. I paid $2000 for it along with a Printer that typed at 60 words a minute for $400. I was able to write a program for it that sent morse code for me when calling out a CQ and answering a Call from some one giving my QTH location. I used the the pause button, making it a short pause for the dit and a longer pause for the dot. I used the orface on the back that was used to turn on the tape recorder to open and close the key on my computer. It worked very well. I also used it to send RTTY Radio Teletype. I kept it until 1997 and it partly burned up in a fire. I had all my set of books laid out one month at a time on a Floppy. My Insurance company reembursed me for $1000 which I used to buy a new computer. Some great memories with my Sol 20.

(Submitted February 12, 2011 20:54:58 by Dallas Foster)

In 1976 another Industrial Engineer & I purchased 3 SOL 20 computers with 48K of RAM and monitored 4 paint production lines painting Chev & Pontiac bumper facias 16 car colors for GM. A production schedule was fed in & sensors kept track of colors painted, parts rejected. Reports were printed on demand on a 2nd SOL. 9 remote monitors ran off the screen, 1 for each paint booth, 1 for each inspector & 1 to the paint mix room. The system ran 3 years without any missed shipping deadlines. This was the first computer controlled monitoring system in a GM factory.

(Submitted April 2, 2010 03:39:24 by Steve Bendon)

can someone tell me how to hook one up to a reg monitor,I made a cable and tried a rf mod box but have had no luck.mine powers up but i dont know how it well it works without seeing a picture. thanks steve

(Submitted February 25, 2010 17:34:52 by Cameron Cooper)

I've had my eye out for a Sol for quite a long time. I'd love to get my hands on one to tinker with. If there are any out there looking for a friendly new home, let me know!

(Submitted September 12, 2009 02:43:07 by Larry Brown)

I went to work as an electronics test set repair technician for Western Electric in 1969. I couldn't get them to send me to classes on microcomputers, so in the mid 1970s,I bought blank Processor Technology boards, a Vector case, and wired everything from scratch. I built my own front panel,wired the backplane and power supply,and built up the blank boards. I modified a 12 inch Radio Shack television set and also used a discarded DEC keyboard. I always wanted a Sol-20, but I couldn't afford it then.If someone wants to give one a good home, contact me. I still have the system I built at home. I bought almost all my parts at Data Domain near Bloomington,IN. They gave me a lot of manuals and software. Western Electric finally sent me to DEC school for the PDP-11 in 1979 after I had been repairing computers for 10 years. I got both the software programming and hardware courses.

(Submitted April 28, 2009 08:57:47 by (a href=mailto:)Mortar(/a))

When I saw this for the first time in one of the many mom-and-pop computer stores of the day, my immediate reaction was, Oooo, pretty. It was certainly the best looking of the bunch. I also thought the keyboard had the best feel of the bunch, too.

(Submitted January 10, 2009 19:00:29 by Dr. Michael Miller)

I built a Sol-20 in 1978 in college. Still have it, still works, and it needs a good home. Email me for pictures and inventory of original manuals and software, including most every Proteus newsletter, offer to share shipping from New York City and she's yours to treasure for another 30 years. Includes original Panasonic TV used as monitor, 5.25 disk drives, casette tape recorder for I/O, original software plus more. I can't bring myself to throw her away.

(Submitted October 22, 2008 22:20:26 by (a Deuel(/a))

Sort of offtopic, but you can read an interview with Rick from below, talk about his SOL-20 computer and his career in programming. Check it out here: .html

(Submitted July 5, 2008 21:52:43 by Thom)

You might enjoy this article in the 1982 Atlantic Monthly. I found this page to look up the computer he is using,

(Submitted February 27, 2008 14:06:56 by Howard Dimmick)

I built one of these from a kit in 1978

(Submitted April 13, 2007 14:19:11 by Rick)

My goodness, a Sol-20. Sure brings back memories. I remember reverse engineering the TARG game so I could make more things drop faster from the sky (run up a high score). In 1977-1978 I wrote a 4k chess program in 8080. I never commercialized the program, but it beat Boris (early 80's chess playing computer). My obsession with my Sol-20 inspired my switch to software engineering (I was a designer/programmer -- video games and R&D -- for 30 years) from teacher of Mathematics.

(Submitted March 31, 2007 05:44:41 by Jeff Smith)

In 1975 I saw an article in an issue of Popular Electronics about the sol-20. A computer, in kit form too! Move over Heathkit. The soldering and such went pretty smoothly but we missed an solder joint.Just one.Out of about 2000 of them.Finally it jumped out at us. And when the rosin cloud drifted away we plugged her in again and a cursor was born.

(Submitted January 30, 2007 21:23:16 by Gary Bisaga)

Man, I learned how to program in assembly language from the Sol-20. I built mine (with my dad's help) when I was 15. I used to lay on my bed and pore over the assembly language listing of the Personality Module for hours and hours - and I still remember some of the comments in that listing. Man, what a waste of good brain cells. :-)

(Submitted November 29, 2006 06:01:53 by Bob C. Hookham)

I built the SOL-20 as a school project in 1976- 77, as an alternative to the time-share computor that our high school was renting. I was the Lead tech (17 yrs old) of the three of us who built it. The net result was that our high school was so impressed with it, that the following school year they bought 15 of the new Apples the were being marketed at that time. Within 3 yrs, I was told that my HS had purchased over 200 computers for student use, in a HS of only 1200 students. Our electronics program in the '70's and early '80's was so far ahead of the local Jr college, that students who were taught under a specific instructor were given FULL credit towards their EE Degree. Thanks for the pictures, they bring back a lot of memories (a GOOD thing). BCH

(Submitted May 31, 2005 17:41:35 by Mac Goodell)

Your SOL-20 looks great. I have one stored in my garage. My students and I raised the funds, and assembled the kit for a long time, and it worked great. We used a regular TV set (20 inch) for demostrations. How frightened most people were when we ran Eliza and analyzed peoples' psyches.I used the machine to teach Basic programming, and some students wrote and sold game programs to software venders. It would be a celebration whenever we discovered another $250, and bought a kit to make another 64K memory card! If anyone ever expresses interest in the SOL-20, for a museum display, you could have them contact me at m-and-

(Submitted April 15, 2005 16:14:14 by Larry)

The SO-239 connector is composite video output for the monitor.

(Submitted April 4, 2005 18:36:46 by Tandy)

I wonder what the SO-239 connector is for? Looking at all these old computers kinda makes me appreciate PCI and Plug n Play. :-)

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