📐 Screen Capacity
Real IBM cards had 80 columns × 12 rows. At a readable hole size on screen, 32 columns fit comfortably — each column holds 8 bits = 1 byte = 1 ASCII character.
🔢 Bit Positions
Top row = bit 7 (value 128). Bottom row = bit 0 (value 1). Add all punched row values together to get the decimal number, then look up the ASCII table.
⌨️ Keypunch Machine
Programmers typed on a machine that punched holes instead of ink. One card per line of code. A 500-line program = 500 physical cards. Drop them — start over.
🔗 Binary ↔ ASCII
Letter 'H' = 72 = 01001000. Letter 'A' = 65 = 01000001. Space = 32 = 00100000. Every character you type is secretly a number in disguise.