SOLIDAC
(the SOLID-state Automatic Computer)
was a unique mini-computer at Glasgow University,
designed and constructed during 1959-63.
It was the first computer to be built in Scotland.
At that time most computers were monsters,
shut away in air-conditioned seclusion,
and access was jealously guarded by a cabal of all-powerful operations staff.
With 1K (yes, one K!) of 20-bit words,
and a clock rate of 30kHz (yes, 30 k Hz!),
the desk-sized SOLIDAC:
was a flea in the company of elephants;
but it was intended specifically to provide undergraduates with hands-on computer experience.
With its combination of simplicity, economy, elegance, and completeness, the instruction set of SOLIDAC shames many architectures of much more recent design. Solidac: An Early Minicomputer for Teaching Purposes is a short paper by Paul (P.A.V.) Thomas, the principal designer of the SOLIDAC, outlining something of its rationale, architecture, and history.
Here is the programming part of the SOLIDAC Users’ Manual, as an OCRed PDF. And here is the part of the manual that describes how to (physically) operate the machine, and use the bootstrap loader. The latter, held in 96 words of read-only storage, is a little miracle of software miniaturization. The spiritual descendent of Wheeler’s ‘Initial Orders’ for the EDSAC, it functions as a bootstrap, relocating loader, and ‘femto-kernel’.
An element of purely personal history intrudes here, as SOLIDAC was the first computer I had the chance to operate. In 1965 a public lecture was given by Tom (T.H.) O’Beirne, on the topic Music, Numbers, and Computers (the Bull. Inst. Math. Appl. later published a paper with the same title). Tom O’Beirne was a ‘character’ of the old school, such as one seldom encounters these days. I already knew him by reputation, through his recreational mathematics column in the New Scientist magazine, Puzzles and Paradoxes. Since music, numbers, and computers were three of my great interests, I attended his lecture. At the end of the talk Tom invited the audience to a demonstration. I took part, and was allowed to flick handswitches and enter numbers on the SOLIDAC console, which had a telephone dial for the easy input of decimal data. This was quite a thrill for a nerdy 17-year-old, half a century ago!
I capitalised on this experience by writing an essay on ‘What I did at the weekend’ for my Spanish class homework, entitled Música, números y máquinas de computación. The Spanish word for computer, ordenador, had not yet found its way into elementary dictionaries.
Many years later my long–term interest in the musical application of computers led to research collaborations with Crawford Tait and Cordy Hall, resulting in the publications linked from here.
Thanks to Tom’s virtuoso programming in machine code, SOLIDAC was capable of impressive feats in the automated composition and performance of music. This resulted in the release of an LP album that was reviewed in Gramophone. In later years Tom joined the Department of Computing Science at Glasgow University, where he lavished care on SOLIDAC, keeping it operational well beyond its natural lifespan.
Here is a short list of SOLIDAC-related publications.
A selection of Tom O’Beirne’s recreational mathematics articles was later published in book form:
See also:
