The Z-80 has a 4-bit ALU. Here’s how it works. (righto.com)The 8-bit Z-80 processor is famed for use in many early personal computers such the Osborne 1, TRS-80, and Sinclair ZX Spectrum, and it is still used in embedded systems and TI graphing calculators. I had always assumed that the ALU (arithmetic-logic unit) in the Z-80 was 8 bits wide, like just about every other 8-bit processor. But while reverse-engineering the Z-80, I was shocked to discover the ALU is only 4 bits wide! The founders of Zilog mentioned the 4-bit ALU in a very interesting discussion at the Computer History Museum, so it’s not exactly a secret, but it’s not well-known either.
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Frederick Douglass (Wikipedia)Frederick Douglass (born Frederick Augustus Washington Bailey, c. February 1817 or 1818 – February 20, 1895) was an American social reformer, abolitionist, orator, writer, and statesman. After escaping from slavery in Maryland, he became a national leader of the abolitionist movement in Massachusetts and New York, becoming famous for his oratory and incisive antislavery writings. Accordingly, he was described by abolitionists in his time as a living counterexample to enslavers’ arguments that enslaved people lacked the intellectual capacity to function as independent American citizens. Northerners at the time found it hard to believe that such a great orator had once been enslaved. It was in response to this disbelief that Douglass wrote his first autobiography.