// FROM THE METAL //

The layer beneath the abstraction.

Twenty years of programming advice — unroll your loops, avoid the branch, mind the cache — passed down as folklore you take on trust. Drop to a machine small enough to hold in your head, count the cycles by hand, and the folklore turns into something you can see. Each piece takes one familiar rule down to the metal.

Performance · 6502

Why "unroll your loops" is real advice

Twenty-year-old advice, finally visible. On a 6502 the loop is just instructions that run every time round — and unrolling deletes them.

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ARITHMETIC · 6502

When 255 + 1 = 0

255 + 1 = 0 with a carry, $80 is both 128 and −128, and abs(MIN) comes back negative — two's complement, shown whole in three 6502 instructions.

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ARITHMETIC · Z80

Why everything is a power of two

The Z80 can't multiply, so it has to show you why a power-of-two capacity makes modulo free and 1,024 is engineering, not superstition.

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ARCHITECTURE · 68000

"Stack overflow" is a real place

On the 68000 the stack is just A7 walking down through RAM — watch the pointer move and stack frames, recursion's cost and 'stack overflow' all turn literal.

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// 10 more in the series — a new one every week //