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Famous reverse engineer and laptop historian Ken Shirriff has turned his consideration to a board designed for the Univac 1004 within the Sixties — figuring out the bizarre part as an AND-OR-INVERT logic board with some unknown options.
“The IBM 1401 workforce on the Laptop Historical past Museum accumulates a whole lot of thriller elements from donations and different sources,” Shirriff explains of the origins of his newest board. “Whereas going by way of a field, we got here throughout [this] uncommon circuit board.
“At first, it appeared like an IBM SMS (Customary Modular System) card, the constructing block of IBM’s computer systems of the late Fifties and early Sixties. Nonetheless, this board is bigger, has double-sided wiring, the connector is totally different, and the labeling is totally different.”
Ken Shirriff has recognized this uncommon board as a Univac 1004 accent, and reverse engineered its utility. (📷: Ken Shirriff)
The board, which has an edge connector to 1 facet, was recognized by Robert Garner as a plug-in for the Univac 1004 plugboard-based “Card Processor” — able to operating applications of as much as 31 steps in size, “coded” by way of using a tangle of wires on a plugboard.
“The perform of the board wasn’t instantly apparent and we had varied theories of what it’d do. To seek out out, I reverse engineered the board by tracing out the circuitry,” Shirriff writes. “The board has 32 diodes, which looks like loads, in addition to resistors, transistors, and capacitors. The transistors usually are not silicon transistors, however germanium PNP transistor.”
The results of cautious evaluation: The identification of the board as an AND-OR-INVERT logic board, carried out in diode-transistor logic (DTL). “That’s, varied inputs are ANDed collectively, the AND outcomes are then ORed collectively, and eventually the result’s inverted,” Shirriff explains.
The board has now been traced out to a full schematic, although some features are nonetheless of unknown function. (📷: Ken Shirriff)
“After tracing out the board’s logic,” he continues, “I acknowledged that it carried out a full adder. The board has just a few extra circuits together with the complete adder circuit. It contains an inverter circuit. The board additionally has 4 inputs which can be ANDed, topic to the carry worth.
“Lastly, the board additionally has a disable enter that blocks the outputs. With out understanding extra in regards to the circuitry, I am unable to decide the function of those circuits.”
Shirrif’s full write-up, full with schematics, is out there on his web site.
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