Ken Shirriff's blog

Computer history, restoring vintage computers, IC reverse engineering, and whatever

1950's tax preparation: plugboard programming with an IBM 403 Accounting Machine

Long before computers existed, businesses used electromechanical accounting machines for data processing. These one-ton accounting machines ...

Inside the vintage 74181 ALU chip: how it works and why it's so strange

The 74181 ALU (arithmetic/logic unit) chip powered many of the minicomputers of the 1970s: it provided fast 4-bit arithmetic and logic funct...

Analyzing the vintage 8008 processor from die photos: its unusual counters

The revolutionary Intel 8008 microprocessor is 45 years old today (March 13, 2017), so I figured it's time for a blog post on reverse-en...

Reverse-engineering the surprisingly advanced ALU of the 8008 microprocessor

A computer's arithmetic-logic unit (ALU) is the heart of the processor, performing arithmetic and logic operations on data. If you'v...

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