Click any square to punch a hole or fill one in. The same holes, read a different way, weave a pattern:
The same card, two jobs
Feed the roll past a reader and every hole is a note: which row it is in says which note, and how far along says when.
Feed the same card into a loom and every hole is a thread lifted or left down, so the pattern below is the cloth those holes would weave.
Nothing about the holes changed. What changed is the machine reading them, which is the whole idea of a code made of position.
Weaving to computers, in three steps
1801. Joseph Marie Jacquard puts punched cards into a loom. A pattern that took a skilled weaver weeks to set up becomes a stack of cards anybody can load. The cards are the design, and the loom simply obeys them.
The 1830s. Charles Babbage sees this and takes the idea somewhere strange: if cards can tell a loom what to weave, cards can tell a machine what to calculate. Ada Lovelace, writing about his engine, says it weaves algebraic patterns as the loom weaves flowers and leaves.
Then a century of them. Punched cards ran censuses, payrolls and the first computers. Programs were stacks of cards, and dropping the stack was a catastrophe, which is why programmers drew a diagonal line across the top edge.
Holes in card, standing for something, in an order that matters. That is a piano roll, a loom, a program and a message, and it is the reason this page sits in the signals section rather than the ciphers.
The music box Hexadecimal Back to signals