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Inside the 74181 ALU chip: die photos and reverse engineering

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What's inside a TTL chip? To find out, I opened up a 74181 ALU chip, took high-resolution die photos, and reverse-engineered the chip. 1 In...

What's inside a TTL chip? To find out, I opened up a 74181 ALU chip, took high-resolution die photos, and reverse-engineered the chip.1 Inside I found several types of gates, implemented with interesting circuitry and unusual transistors. The 74181 was a popular chip in the 1970s used to perform calculations in the arithmetic-logic unit (ALU) of minicomputers. It is a moderately complex chip containing about 67 gates and 170 transistors3, implemented using fast and popular TTL (transistor-transistor logic) circuitry. The 74181 die photo is below. (Click the image for a high-resolution…

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