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This 1960s-era training film produced by Audio Productions, Inc. for the United States Navy discusses the different types of logic circuits used in early computers. This film was one of a 5-part series from Bell Labs designed to explain basic computing elements. The film is marked as “Unclassified.” The film begins in black and white with women holding rolls of punch cards next to early computers, then transitions to a shot of the first electronic digital computer invented in 1946, called the ENIAC (Electronic Numerical Integrator and Computer) (0:48), made of electromechanical relays and vacuum tubes. A man works at an early computer switchboard (1:09). Solid state electronic components, semiconductor diodes, and transistors are shown in color (1:14). A man pulls out a semiconductor diode and explains the different parts and how they conduct current (1:40). Transistors and diodes like these provided an advantage over early computers in size, reliability, and power consumption. The film then goes over several different types of logic element circuits and explains how they operate: 1) Diode circuits, 2) Transistor circuits, 3) Inverters, and 4) Flip-flops. Diode circuits (2:15) function as and/or gates. A diagram of an “and” gate with inputs and outputs is explained (2:28). Diodes and a resistor for the “and” circuit are diagrammed, and a voiceover narrates how they function at different levels of current (3:15). Then a diagram of an “or” gate is shown (5:22). An “or” gate functions as a mixer or buffer. How the “or” gate behaves with different inputs and outputs is explained (5:34). An “or” circuit differs from an “and” circuit in that the cathodes are connected to the resistor, and returns to a negative, not positive, resistor (5:49). Transistor circuits (7:24) are made of three components: an emitter, a base, and a collector. The most common type of transistor circuit used in a computer is a P-N-P (positive-negative-positive) circuit (8:05). A diagram of a P-N-P transistor is drawn and a voiceover explains how it functions as a switch at different voltages (8:50). A transistor “and” gate is shown (9:03), and combinations of various inputs are explained. Binary 1 is associated with a low negative voltage, and binary 0 is associated with zero or low positive voltage. Then a transistor “or” gate is shown (10:28), which differs from the “and” gate because the transistors are in parallel with each other, creating parallel switches. A diagram of an inverter, which looks like a black arrow with a white circle in the middle, is shown (11:22). An inverter inverts the current, changing a high input to low output or vice versa. Different parts of the diagram are highlighted in white as the voiceover explains their function (12:27). A diagram of a “nor” gate is shown (12:45), which delivers 0 as an output except for when both inputs are 0, creating a 1 output. Then a “nor” circuit is shown, which is similar to the inverter circuit except it has 2 inputs (13:10). A “flip-flop” type of gate is shown (14:31), named because it alternates producing “set” or “reset” outputs. Pulses are applied alternately to the “set” and “reset” inputs, producing alternate “set” and “reset” outputs. The diagram shows a rectangle with “S” for set, “R” for reset, “O” for output, and “I” for input in the 4 corners. Flip-flop circuit functions are explained in more detail (15:00). At 16:45, the film returns to showing color footage of a man moving a shelf of semiconductor diodes. The slogan “Sea Power for Security” is shown in the closing credits (17:02).
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